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package java.lang.invoke;

import java.lang.reflect.*;
import java.util.BitSet;
import java.util.List;
import java.util.Arrays;

import sun.invoke.util.ValueConversions;
import sun.invoke.util.VerifyAccess;
import sun.invoke.util.Wrapper;
import sun.reflect.CallerSensitive;
import sun.reflect.Reflection;
import sun.reflect.misc.ReflectUtil;
import sun.security.util.SecurityConstants;
import java.lang.invoke.LambdaForm.BasicType;

import static java.lang.invoke.LambdaForm.BasicType.*;
import static java.lang.invoke.MethodHandleStatics.*;
import static java.lang.invoke.MethodHandleImpl.Intrinsic;
import static java.lang.invoke.MethodHandleNatives.Constants.*;

import java.util.concurrent.ConcurrentHashMap;

/**
 * This class consists exclusively of static methods that operate on or return method handles. They
 * fall into several categories: <ul> <li>Lookup methods which help create method handles for
 * methods and fields. <li>Combinator methods, which combine or transform pre-existing method
 * handles into new ones. <li>Other factory methods to create method handles that emulate other
 * common JVM operations or control flow patterns. </ul> <p>
 *
 * @author John Rose, JSR 292 EG
 * @since 1.7
 */
public class MethodHandles {

  private MethodHandles() {
  }  // do not instantiate

  private static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();

  static {
    MethodHandleImpl.initStatics();
  }
  // See IMPL_LOOKUP below.

  //// Method handle creation from ordinary methods.

  /**
   * Returns a {@link Lookup lookup object} with full capabilities to emulate all supported bytecode
   * behaviors of the caller. These capabilities include <a href="MethodHandles.Lookup.html#privacc">private
   * access</a> to the caller. Factory methods on the lookup object can create <a
   * href="MethodHandleInfo.html#directmh">direct method handles</a> for any member that the caller
   * has access to via bytecodes, including protected and private fields and methods. This lookup
   * object is a <em>capability</em> which may be delegated to trusted agents. Do not store it in
   * place where untrusted code can access it. <p> This method is caller sensitive, which means that
   * it may return different values to different callers. <p> For any given caller class {@code C},
   * the lookup object returned by this call has equivalent capabilities to any lookup object
   * supplied by the JVM to the bootstrap method of an <a href="package-summary.html#indyinsn">invokedynamic
   * instruction</a> executing in the same caller class {@code C}.
   *
   * @return a lookup object for the caller of this method, with private access
   */
  @CallerSensitive
  public static Lookup lookup() {
    return new Lookup(Reflection.getCallerClass());
  }

  /**
   * Returns a {@link Lookup lookup object} which is trusted minimally.
   * It can only be used to create method handles to
   * publicly accessible fields and methods.
   * <p>
   * As a matter of pure convention, the {@linkplain Lookup#lookupClass lookup class}
   * of this lookup object will be {@link java.lang.Object}.
   *
   * <p style="font-size:smaller;">
   * <em>Discussion:</em>
   * The lookup class can be changed to any other class {@code C} using an expression of the form
   * {@link Lookup#in publicLookup().in(C.class)}.
   * Since all classes have equal access to public names,
   * such a change would confer no new access rights.
   * A public lookup object is always subject to
   * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
   * Also, it cannot access
   * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
   *
   * @return a lookup object which is trusted minimally
   */
  public static Lookup publicLookup() {
    return Lookup.PUBLIC_LOOKUP;
  }

  /**
   * Performs an unchecked "crack" of a
   * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
   * The result is as if the user had obtained a lookup object capable enough
   * to crack the target method handle, called
   * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
   * on the target to obtain its symbolic reference, and then called
   * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
   * to resolve the symbolic reference to a member.
   * <p>
   * If there is a security manager, its {@code checkPermission} method
   * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
   *
   * @param <T> the desired type of the result, either {@link Member} or a subtype
   * @param target a direct method handle to crack into symbolic reference components
   * @param expected a class object representing the desired result type {@code T}
   * @return a reference to the method, constructor, or field object
   * @throws SecurityException if the caller is not privileged to call {@code setAccessible}
   * @throws NullPointerException if either argument is {@code null}
   * @throws IllegalArgumentException if the target is not a direct method handle
   * @throws ClassCastException if the member is not of the expected type
   * @since 1.8
   */
  public static <T extends Member> T
  reflectAs(Class<T> expected, MethodHandle target) {
    SecurityManager smgr = System.getSecurityManager();
    if (smgr != null) {
      smgr.checkPermission(ACCESS_PERMISSION);
    }
    Lookup lookup = Lookup.IMPL_LOOKUP;  // use maximally privileged lookup
    return lookup.revealDirect(target).reflectAs(expected, lookup);
  }

  // Copied from AccessibleObject, as used by Method.setAccessible, etc.:
  static final private java.security.Permission ACCESS_PERMISSION =
      new ReflectPermission("suppressAccessChecks");

  /**
   * A <em>lookup object</em> is a factory for creating method handles, when the creation requires
   * access checking. Method handles do not perform access checks when they are called, but rather
   * when they are created. Therefore, method handle access restrictions must be enforced when a
   * method handle is created. The caller class against which those restrictions are enforced is
   * known as the {@linkplain #lookupClass lookup class}. <p> A lookup class which needs to create
   * method handles will call {@link MethodHandles#lookup MethodHandles.lookup} to create a factory
   * for itself. When the {@code Lookup} factory object is created, the identity of the lookup class
   * is determined, and securely stored in the {@code Lookup} object. The lookup class (or its
   * delegates) may then use factory methods on the {@code Lookup} object to create method handles
   * for access-checked members. This includes all methods, constructors, and fields which are
   * allowed to the lookup class, even private ones.
   *
   * <h1><a name="lookups"></a>Lookup Factory Methods</h1> The factory methods on a {@code Lookup}
   * object correspond to all major use cases for methods, constructors, and fields. Each method
   * handle created by a factory method is the functional equivalent of a particular <em>bytecode
   * behavior</em>. (Bytecode behaviors are described in section 5.4.3.5 of the Java Virtual Machine
   * Specification.) Here is a summary of the correspondence between these factory methods and the
   * behavior the resulting method handles: <table border=1 cellpadding=5 summary="lookup method
   * behaviors"> <tr> <th><a name="equiv"></a>lookup expression</th> <th>member</th> <th>bytecode
   * behavior</th> </tr> <tr> <td>{@link java.lang.invoke.MethodHandles.Lookup#findGetter
   * lookup.findGetter(C.class,"f",FT.class)}</td> <td>{@code FT f;}</td><td>{@code (T)
   * this.f;}</td> </tr> <tr> <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter
   * lookup.findStaticGetter(C.class,"f",FT.class)}</td> <td>{@code static}<br>{@code FT
   * f;}</td><td>{@code (T) C.f;}</td> </tr> <tr> <td>{@link java.lang.invoke.MethodHandles.Lookup#findSetter
   * lookup.findSetter(C.class,"f",FT.class)}</td> <td>{@code FT f;}</td><td>{@code this.f =
   * x;}</td> </tr> <tr> <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter
   * lookup.findStaticSetter(C.class,"f",FT.class)}</td> <td>{@code static}<br>{@code FT
   * f;}</td><td>{@code C.f = arg;}</td> </tr> <tr> <td>{@link java.lang.invoke.MethodHandles.Lookup#findVirtual
   * lookup.findVirtual(C.class,"m",MT)}</td> <td>{@code T m(A*);}</td><td>{@code (T)
   * this.m(arg*);}</td> </tr> <tr> <td>{@link java.lang.invoke.MethodHandles.Lookup#findStatic
   * lookup.findStatic(C.class,"m",MT)}</td> <td>{@code static}<br>{@code T m(A*);}</td><td>{@code
   * (T) C.m(arg*);}</td> </tr> <tr> <td>{@link java.lang.invoke.MethodHandles.Lookup#findSpecial
   * lookup.findSpecial(C.class,"m",MT,this.class)}</td> <td>{@code T m(A*);}</td><td>{@code (T)
   * super.m(arg*);}</td> </tr> <tr> <td>{@link java.lang.invoke.MethodHandles.Lookup#findConstructor
   * lookup.findConstructor(C.class,MT)}</td> <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
   * </tr> <tr> <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter
   * lookup.unreflectGetter(aField)}</td> <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT)
   * aField.get(thisOrNull);}</td> </tr> <tr> <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter
   * lookup.unreflectSetter(aField)}</td> <td>({@code static})?<br>{@code FT f;}</td><td>{@code
   * aField.set(thisOrNull, arg);}</td> </tr> <tr> <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect
   * lookup.unreflect(aMethod)}</td> <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T)
   * aMethod.invoke(thisOrNull, arg*);}</td> </tr> <tr> <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor
   * lookup.unreflectConstructor(aConstructor)}</td> <td>{@code C(A*);}</td><td>{@code (C)
   * aConstructor.newInstance(arg*);}</td> </tr> <tr> <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect
   * lookup.unreflect(aMethod)}</td> <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T)
   * aMethod.invoke(thisOrNull, arg*);}</td> </tr> </table>
   *
   * Here, the type {@code C} is the class or interface being searched for a member, documented as a
   * parameter named {@code refc} in the lookup methods. The method type {@code MT} is composed from
   * the return type {@code T} and the sequence of argument types {@code A*}. The constructor also
   * has a sequence of argument types {@code A*} and is deemed to return the newly-created object of
   * type {@code C}. Both {@code MT} and the field type {@code FT} are documented as a parameter
   * named {@code type}. The formal parameter {@code this} stands for the self-reference of type
   * {@code C}; if it is present, it is always the leading argument to the method handle invocation.
   * (In the case of some {@code protected} members, {@code this} may be restricted in type to the
   * lookup class; see below.) The name {@code arg} stands for all the other method handle
   * arguments. In the code examples for the Core Reflection API, the name {@code thisOrNull} stands
   * for a null reference if the accessed method or field is static, and {@code this} otherwise. The
   * names {@code aMethod}, {@code aField}, and {@code aConstructor} stand for reflective objects
   * corresponding to the given members. <p> In cases where the given member is of variable arity
   * (i.e., a method or constructor) the returned method handle will also be of {@linkplain
   * MethodHandle#asVarargsCollector variable arity}. In all other cases, the returned method handle
   * will be of fixed arity. <p style="font-size:smaller;"> <em>Discussion:</em> The equivalence
   * between looked-up method handles and underlying class members and bytecode behaviors can break
   * down in a few ways: <ul style="font-size:smaller;"> <li>If {@code C} is not symbolically
   * accessible from the lookup class's loader, the lookup can still succeed, even when there is no
   * equivalent Java expression or bytecoded constant. <li>Likewise, if {@code T} or {@code MT} is
   * not symbolically accessible from the lookup class's loader, the lookup can still succeed. For
   * example, lookups for {@code MethodHandle.invokeExact} and {@code MethodHandle.invoke} will
   * always succeed, regardless of requested type. <li>If there is a security manager installed, it
   * can forbid the lookup on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see
   * below</a>). By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
   * constant is not subject to security manager checks. <li>If the looked-up method has a <a
   * href="MethodHandle.html#maxarity">very large arity</a>, the method handle creation may fail,
   * due to the method handle type having too many parameters. </ul>
   *
   * <h1><a name="access"></a>Access checking</h1> Access checks are applied in the factory methods
   * of {@code Lookup}, when a method handle is created. This is a key difference from the Core
   * Reflection API, since {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
   * performs access checking against every caller, on every call. <p> All access checks start from
   * a {@code Lookup} object, which compares its recorded lookup class against all requests to
   * create method handles. A single {@code Lookup} object can be used to create any number of
   * access-checked method handles, all checked against a single lookup class. <p> A {@code Lookup}
   * object can be shared with other trusted code, such as a metaobject protocol. A shared {@code
   * Lookup} object delegates the capability to create method handles on private members of the
   * lookup class. Even if privileged code uses the {@code Lookup} object, the access checking is
   * confined to the privileges of the original lookup class. <p> A lookup can fail, because the
   * containing class is not accessible to the lookup class, or because the desired class member is
   * missing, or because the desired class member is not accessible to the lookup class, or because
   * the lookup object is not trusted enough to access the member. In any of these cases, a {@code
   * ReflectiveOperationException} will be thrown from the attempted lookup.  The exact class will
   * be one of the following: <ul> <li>NoSuchMethodException &mdash; if a method is requested but
   * does not exist <li>NoSuchFieldException &mdash; if a field is requested but does not exist
   * <li>IllegalAccessException &mdash; if the member exists but an access check fails </ul> <p> In
   * general, the conditions under which a method handle may be looked up for a method {@code M} are
   * no more restrictive than the conditions under which the lookup class could have compiled,
   * verified, and resolved a call to {@code M}. Where the JVM would raise exceptions like {@code
   * NoSuchMethodError}, a method handle lookup will generally raise a corresponding checked
   * exception, such as {@code NoSuchMethodException}. And the effect of invoking the method handle
   * resulting from the lookup is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
   * to executing the compiled, verified, and resolved call to {@code M}. The same point is true of
   * fields and constructors. <p style="font-size:smaller;"> <em>Discussion:</em> Access checks only
   * apply to named and reflected methods, constructors, and fields. Other method handle creation
   * methods, such as {@link MethodHandle#asType MethodHandle.asType}, do not require any access
   * checks, and are used independently of any {@code Lookup} object. <p> If the desired member is
   * {@code protected}, the usual JVM rules apply, including the requirement that the lookup class
   * must be either be in the same package as the desired member, or must inherit that member. (See
   * the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.) In addition, if the
   * desired member is a non-static field or method in a different package, the resulting method
   * handle may only be applied to objects of the lookup class or one of its subclasses. This
   * requirement is enforced by narrowing the type of the leading {@code this} parameter from {@code
   * C} (which will necessarily be a superclass of the lookup class) to the lookup class itself. <p>
   * The JVM imposes a similar requirement on {@code invokespecial} instruction, that the receiver
   * argument must match both the resolved method <em>and</em> the current class.  Again, this
   * requirement is enforced by narrowing the type of the leading parameter to the resulting method
   * handle. (See the Java Virtual Machine Specification, section 4.10.1.9.) <p> The JVM represents
   * constructors and static initializer blocks as internal methods with special names ({@code
   * "<init>"} and {@code "<clinit>"}). The internal syntax of invocation instructions allows them
   * to refer to such internal methods as if they were normal methods, but the JVM bytecode verifier
   * rejects them. A lookup of such an internal method will produce a {@code NoSuchMethodException}.
   * <p> In some cases, access between nested classes is obtained by the Java compiler by creating
   * an wrapper method to access a private method of another class in the same top-level
   * declaration. For example, a nested class {@code C.D} can access private members within other
   * related classes such as {@code C}, {@code C.D.E}, or {@code C.B}, but the Java compiler may
   * need to generate wrapper methods in those related classes.  In such cases, a {@code Lookup}
   * object on {@code C.E} would be unable to those private members. A workaround for this
   * limitation is the {@link Lookup#in Lookup.in} method, which can transform a lookup on {@code
   * C.E} into one on any of those other classes, without special elevation of privilege. <p> The
   * accesses permitted to a given lookup object may be limited, according to its set of {@link
   * #lookupModes lookupModes}, to a subset of members normally accessible to the lookup class. For
   * example, the {@link MethodHandles#publicLookup publicLookup} method produces a lookup object
   * which is only allowed to access public members in public classes. The caller sensitive method
   * {@link MethodHandles#lookup lookup} produces a lookup object with full capabilities relative to
   * its caller class, to emulate all supported bytecode behaviors. Also, the {@link Lookup#in
   * Lookup.in} method may produce a lookup object with fewer access modes than the original lookup
   * object.
   *
   * <p style="font-size:smaller;"> <a name="privacc"></a> <em>Discussion of private access:</em> We
   * say that a lookup has <em>private access</em> if its {@linkplain #lookupModes lookup modes}
   * include the possibility of accessing {@code private} members. As documented in the relevant
   * methods elsewhere, only lookups with private access possess the following capabilities: <ul
   * style="font-size:smaller;"> <li>access private fields, methods, and constructors of the lookup
   * class <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller
   * sensitive</a> methods, such as {@code Class.forName} <li>create method handles which {@link
   * Lookup#findSpecial emulate invokespecial} instructions <li>avoid <a
   * href="MethodHandles.Lookup.html#secmgr">package access checks</a> for classes accessible to the
   * lookup class <li>create {@link Lookup#in delegated lookup objects} which have private access to
   * other classes within the same package member </ul> <p style="font-size:smaller;"> Each of these
   * permissions is a consequence of the fact that a lookup object with private access can be
   * securely traced back to an originating class, whose <a href="MethodHandles.Lookup.html#equiv">bytecode
   * behaviors</a> and Java language access permissions can be reliably determined and emulated by
   * method handles.
   *
   * <h1><a name="secmgr"></a>Security manager interactions</h1> Although bytecode instructions can
   * only refer to classes in a related class loader, this API can search for methods in any class,
   * as long as a reference to its {@code Class} object is available.  Such cross-loader references
   * are also possible with the Core Reflection API, and are impossible to bytecode instructions
   * such as {@code invokestatic} or {@code getfield}. There is a {@linkplain
   * java.lang.SecurityManager security manager API} to allow applications to check such
   * cross-loader references. These checks apply to both the {@code MethodHandles.Lookup} API and
   * the Core Reflection API (as found on {@link java.lang.Class Class}). <p> If a security manager
   * is present, member lookups are subject to additional checks. From one to three calls are made
   * to the security manager. Any of these calls can refuse access by throwing a {@link
   * java.lang.SecurityException SecurityException}. Define {@code smgr} as the security manager,
   * {@code lookc} as the lookup class of the current lookup object, {@code refc} as the containing
   * class in which the member is being sought, and {@code defc} as the class in which the member is
   * actually defined. The value {@code lookc} is defined as <em>not present</em> if the current
   * lookup object does not have <a href="MethodHandles.Lookup.html#privacc">private access</a>. The
   * calls are made according to the following rules: <ul> <li><b>Step 1:</b> If {@code lookc} is
   * not present, or if its class loader is not the same as or an ancestor of the class loader of
   * {@code refc}, then {@link SecurityManager#checkPackageAccess smgr.checkPackageAccess(refcPkg)}
   * is called, where {@code refcPkg} is the package of {@code refc}. <li><b>Step 2:</b> If the
   * retrieved member is not public and {@code lookc} is not present, then {@link
   * SecurityManager#checkPermission smgr.checkPermission} with {@code
   * RuntimePermission("accessDeclaredMembers")} is called. <li><b>Step 3:</b> If the retrieved
   * member is not public, and if {@code lookc} is not present, and if {@code defc} and {@code refc}
   * are different, then {@link SecurityManager#checkPackageAccess smgr.checkPackageAccess(defcPkg)}
   * is called, where {@code defcPkg} is the package of {@code defc}. </ul> Security checks are
   * performed after other access checks have passed. Therefore, the above rules presuppose a member
   * that is public, or else that is being accessed from a lookup class that has rights to access
   * the member.
   *
   * <h1><a name="callsens"></a>Caller sensitive methods</h1> A small number of Java methods have a
   * special property called caller sensitivity. A <em>caller-sensitive</em> method can behave
   * differently depending on the identity of its immediate caller. <p> If a method handle for a
   * caller-sensitive method is requested, the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode
   * behaviors</a> apply, but they take account of the lookup class in a special way. The resulting
   * method handle behaves as if it were called from an instruction contained in the lookup class,
   * so that the caller-sensitive method detects the lookup class. (By contrast, the invoker of the
   * method handle is disregarded.) Thus, in the case of caller-sensitive methods, different lookup
   * classes may give rise to differently behaving method handles. <p> In cases where the lookup
   * object is {@link MethodHandles#publicLookup() publicLookup()}, or some other lookup object
   * without <a href="MethodHandles.Lookup.html#privacc">private access</a>, the lookup class is
   * disregarded. In such cases, no caller-sensitive method handle can be created, access is
   * forbidden, and the lookup fails with an {@code IllegalAccessException}. <p
   * style="font-size:smaller;"> <em>Discussion:</em> For example, the caller-sensitive method
   * {@link java.lang.Class#forName(String) Class.forName(x)} can return varying classes or throw
   * varying exceptions, depending on the class loader of the class that calls it. A public lookup
   * of {@code Class.forName} will fail, because there is no reasonable way to determine its
   * bytecode behavior. <p style="font-size:smaller;"> If an application caches method handles for
   * broad sharing, it should use {@code publicLookup()} to create them. If there is a lookup of
   * {@code Class.forName}, it will fail, and the application must take appropriate action in that
   * case. It may be that a later lookup, perhaps during the invocation of a bootstrap method, can
   * incorporate the specific identity of the caller, making the method accessible. <p
   * style="font-size:smaller;"> The function {@code MethodHandles.lookup} is caller sensitive so
   * that there can be a secure foundation for lookups. Nearly all other methods in the JSR 292 API
   * rely on lookup objects to check access requests.
   */
  public static final class Lookup {

    /**
     * The class on behalf of whom the lookup is being performed.
     */
    private final Class<?> lookupClass;

    /**
     * The allowed sorts of members which may be looked up (PUBLIC, etc.).
     */
    private final int allowedModes;

    /**
     * A single-bit mask representing {@code public} access,
     * which may contribute to the result of {@link #lookupModes lookupModes}.
     * The value, {@code 0x01}, happens to be the same as the value of the
     * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
     */
    public static final int PUBLIC = Modifier.PUBLIC;

    /**
     * A single-bit mask representing {@code private} access,
     * which may contribute to the result of {@link #lookupModes lookupModes}.
     * The value, {@code 0x02}, happens to be the same as the value of the
     * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
     */
    public static final int PRIVATE = Modifier.PRIVATE;

    /**
     * A single-bit mask representing {@code protected} access,
     * which may contribute to the result of {@link #lookupModes lookupModes}.
     * The value, {@code 0x04}, happens to be the same as the value of the
     * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
     */
    public static final int PROTECTED = Modifier.PROTECTED;

    /**
     * A single-bit mask representing {@code package} access (default access),
     * which may contribute to the result of {@link #lookupModes lookupModes}.
     * The value is {@code 0x08}, which does not correspond meaningfully to
     * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
     */
    public static final int PACKAGE = Modifier.STATIC;

    private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE);
    private static final int TRUSTED = -1;

    private static int fixmods(int mods) {
      mods &= (ALL_MODES - PACKAGE);
      return (mods != 0) ? mods : PACKAGE;
    }

    /**
     * Tells which class is performing the lookup.  It is this class against
     * which checks are performed for visibility and access permissions.
     * <p>
     * The class implies a maximum level of access permission,
     * but the permissions may be additionally limited by the bitmask
     * {@link #lookupModes lookupModes}, which controls whether non-public members
     * can be accessed.
     *
     * @return the lookup class, on behalf of which this lookup object finds members
     */
    public Class<?> lookupClass() {
      return lookupClass;
    }

    // This is just for calling out to MethodHandleImpl.
    private Class<?> lookupClassOrNull() {
      return (allowedModes == TRUSTED) ? null : lookupClass;
    }

    /**
     * Tells which access-protection classes of members this lookup object can produce.
     * The result is a bit-mask of the bits
     * {@linkplain #PUBLIC PUBLIC (0x01)},
     * {@linkplain #PRIVATE PRIVATE (0x02)},
     * {@linkplain #PROTECTED PROTECTED (0x04)},
     * and {@linkplain #PACKAGE PACKAGE (0x08)}.
     * <p>
     * A freshly-created lookup object
     * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class}
     * has all possible bits set, since the caller class can access all its own members.
     * A lookup object on a new lookup class
     * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
     * may have some mode bits set to zero.
     * The purpose of this is to restrict access via the new lookup object,
     * so that it can access only names which can be reached by the original
     * lookup object, and also by the new lookup class.
     *
     * @return the lookup modes, which limit the kinds of access performed by this lookup object
     */
    public int lookupModes() {
      return allowedModes & ALL_MODES;
    }

    /**
     * Embody the current class (the lookupClass) as a lookup class
     * for method handle creation.
     * Must be called by from a method in this package,
     * which in turn is called by a method not in this package.
     */
    Lookup(Class<?> lookupClass) {
      this(lookupClass, ALL_MODES);
      // make sure we haven't accidentally picked up a privileged class:
      checkUnprivilegedlookupClass(lookupClass, ALL_MODES);
    }

    private Lookup(Class<?> lookupClass, int allowedModes) {
      this.lookupClass = lookupClass;
      this.allowedModes = allowedModes;
    }

    /**
     * Creates a lookup on the specified new lookup class.
     * The resulting object will report the specified
     * class as its own {@link #lookupClass lookupClass}.
     * <p>
     * However, the resulting {@code Lookup} object is guaranteed
     * to have no more access capabilities than the original.
     * In particular, access capabilities can be lost as follows:<ul>
     * <li>If the new lookup class differs from the old one,
     * protected members will not be accessible by virtue of inheritance.
     * (Protected members may continue to be accessible because of package sharing.)
     * <li>If the new lookup class is in a different package
     * than the old one, protected and default (package) members will not be accessible.
     * <li>If the new lookup class is not within the same package member
     * as the old one, private members will not be accessible.
     * <li>If the new lookup class is not accessible to the old lookup class,
     * then no members, not even public members, will be accessible.
     * (In all other cases, public members will continue to be accessible.)
     * </ul>
     *
     * @param requestedLookupClass the desired lookup class for the new lookup object
     * @return a lookup object which reports the desired lookup class
     * @throws NullPointerException if the argument is null
     */
    public Lookup in(Class<?> requestedLookupClass) {
      requestedLookupClass.getClass();  // null check
      if (allowedModes == TRUSTED)  // IMPL_LOOKUP can make any lookup at all
      {
        return new Lookup(requestedLookupClass, ALL_MODES);
      }
      if (requestedLookupClass == this.lookupClass) {
        return this;  // keep same capabilities
      }
      int newModes = (allowedModes & (ALL_MODES & ~PROTECTED));
      if ((newModes & PACKAGE) != 0
          && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
        newModes &= ~(PACKAGE | PRIVATE);
      }
      // Allow nestmate lookups to be created without special privilege:
      if ((newModes & PRIVATE) != 0
          && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
        newModes &= ~PRIVATE;
      }
      if ((newModes & PUBLIC) != 0
          && !VerifyAccess
          .isClassAccessible(requestedLookupClass, this.lookupClass, allowedModes)) {
        // The requested class it not accessible from the lookup class.
        // No permissions.
        newModes = 0;
      }
      checkUnprivilegedlookupClass(requestedLookupClass, newModes);
      return new Lookup(requestedLookupClass, newModes);
    }

    // Make sure outer class is initialized first.
    static {
      IMPL_NAMES.getClass();
    }

    /**
     * Version of lookup which is trusted minimally.
     * It can only be used to create method handles to
     * publicly accessible members.
     */
    static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, PUBLIC);

    /**
     * Package-private version of lookup which is trusted.
     */
    static final Lookup IMPL_LOOKUP = new Lookup(Object.class, TRUSTED);

    private static void checkUnprivilegedlookupClass(Class<?> lookupClass, int allowedModes) {
      String name = lookupClass.getName();
      if (name.startsWith("java.lang.invoke.")) {
        throw newIllegalArgumentException("illegal lookupClass: " + lookupClass);
      }

      // For caller-sensitive MethodHandles.lookup()
      // disallow lookup more restricted packages
      if (allowedModes == ALL_MODES && lookupClass.getClassLoader() == null) {
        if (name.startsWith("java.") ||
            (name.startsWith("sun.") && !name.startsWith("sun.invoke."))) {
          throw newIllegalArgumentException("illegal lookupClass: " + lookupClass);
        }
      }
    }

    /**
     * Displays the name of the class from which lookups are to be made.
     * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
     * If there are restrictions on the access permitted to this lookup,
     * this is indicated by adding a suffix to the class name, consisting
     * of a slash and a keyword.  The keyword represents the strongest
     * allowed access, and is chosen as follows:
     * <ul>
     * <li>If no access is allowed, the suffix is "/noaccess".
     * <li>If only public access is allowed, the suffix is "/public".
     * <li>If only public and package access are allowed, the suffix is "/package".
     * <li>If only public, package, and private access are allowed, the suffix is "/private".
     * </ul>
     * If none of the above cases apply, it is the case that full
     * access (public, package, private, and protected) is allowed.
     * In this case, no suffix is added.
     * This is true only of an object obtained originally from
     * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
     * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
     * always have restricted access, and will display a suffix.
     * <p>
     * (It may seem strange that protected access should be
     * stronger than private access.  Viewed independently from
     * package access, protected access is the first to be lost,
     * because it requires a direct subclass relationship between
     * caller and callee.)
     *
     * @see #in
     */
    @Override
    public String toString() {
      String cname = lookupClass.getName();
      switch (allowedModes) {
        case 0:  // no privileges
          return cname + "/noaccess";
        case PUBLIC:
          return cname + "/public";
        case PUBLIC | PACKAGE:
          return cname + "/package";
        case ALL_MODES & ~PROTECTED:
          return cname + "/private";
        case ALL_MODES:
          return cname;
        case TRUSTED:
          return "/trusted";  // internal only; not exported
        default:  // Should not happen, but it's a bitfield...
          cname = cname + "/" + Integer.toHexString(allowedModes);
          assert (false) : cname;
          return cname;
      }
    }

    /**
     * Produces a method handle for a static method.
     * The type of the method handle will be that of the method.
     * (Since static methods do not take receivers, there is no
     * additional receiver argument inserted into the method handle type,
     * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
     * The method and all its argument types must be accessible to the lookup object.
     * <p>
     * The returned method handle will have
     * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
     * the method's variable arity modifier bit ({@code 0x0080}) is set.
     * <p>
     * If the returned method handle is invoked, the method's class will
     * be initialized, if it has not already been initialized.
     * <p><b>Example:</b>
     * <blockquote><pre>{@code
     * import static java.lang.invoke.MethodHandles.*;
     * import static java.lang.invoke.MethodType.*;
     * ...
     * MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
     * "asList", methodType(List.class, Object[].class));
     * assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
     * }</pre></blockquote>
     *
     * @param refc the class from which the method is accessed
     * @param name the name of the method
     * @param type the type of the method
     * @return the desired method handle
     * @throws NoSuchMethodException if the method does not exist
     * @throws IllegalAccessException if access checking fails, or if the method is not {@code
     * static}, or if the method's variable arity modifier bit is set and {@code asVarargsCollector}
     * fails
     * @throws SecurityException if a security manager is present and it <a
     * href="MethodHandles.Lookup.html#secmgr">refuses access</a>
     * @throws NullPointerException if any argument is null
     */
    public MethodHandle findStatic(Class<?> refc, String name, MethodType type)
        throws NoSuchMethodException, IllegalAccessException {
      MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
      return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerClass(method));
    }

    /**
     * Produces a method handle for a virtual method. The type of the method handle will be that of
     * the method, with the receiver type (usually {@code refc}) prepended. The method and all its
     * argument types must be accessible to the lookup object. <p> When called, the handle will
     * treat the first argument as a receiver and dispatch on the receiver's type to determine which
     * method implementation to enter. (The dispatching action is identical with that performed by
     * an {@code invokevirtual} or {@code invokeinterface} instruction.) <p> The first argument will
     * be of type {@code refc} if the lookup class has full privileges to access the member.
     * Otherwise the member must be {@code protected} and the first argument will be restricted in
     * type to the lookup class. <p> The returned method handle will have {@linkplain
     * MethodHandle#asVarargsCollector variable arity} if and only if the method's variable arity
     * modifier bit ({@code 0x0080}) is set. <p> Because of the general <a
     * href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
     * instructions and method handles produced by {@code findVirtual}, if the class is {@code
     * MethodHandle} and the name string is {@code invokeExact} or {@code invoke}, the resulting
     * method handle is equivalent to one produced by {@link java.lang.invoke.MethodHandles#exactInvoker
     * MethodHandles.exactInvoker} or {@link java.lang.invoke.MethodHandles#invoker
     * MethodHandles.invoker} with the same {@code type} argument.
     *
     * <b>Example:</b>
     * <blockquote><pre>{@code
     * import static java.lang.invoke.MethodHandles.*;
     * import static java.lang.invoke.MethodType.*;
     * ...
     * MethodHandle MH_concat = publicLookup().findVirtual(String.class,
     * "concat", methodType(String.class, String.class));
     * MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
     * "hashCode", methodType(int.class));
     * MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
     * "hashCode", methodType(int.class));
     * assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
     * assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
     * assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
     * // interface method:
     * MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
     * "subSequence", methodType(CharSequence.class, int.class, int.class));
     * assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
     * // constructor "internal method" must be accessed differently:
     * MethodType MT_newString = methodType(void.class); //()V for new String()
     * try { assertEquals("impossible", lookup()
     * .findVirtual(String.class, "<init>", MT_newString));
     * } catch (NoSuchMethodException ex) { } // OK
     * MethodHandle MH_newString = publicLookup()
     * .findConstructor(String.class, MT_newString);
     * assertEquals("", (String) MH_newString.invokeExact());
     * }</pre></blockquote>
     *
     * @param refc the class or interface from which the method is accessed
     * @param name the name of the method
     * @param type the type of the method, with the receiver argument omitted
     * @return the desired method handle
     * @throws NoSuchMethodException if the method does not exist
     * @throws IllegalAccessException if access checking fails, or if the method is {@code static}
     * or if the method's variable arity modifier bit is set and {@code asVarargsCollector} fails
     * @throws SecurityException if a security manager is present and it <a
     * href="MethodHandles.Lookup.html#secmgr">refuses access</a>
     * @throws NullPointerException if any argument is null
     */
    public MethodHandle findVirtual(Class<?> refc, String name, MethodType type)
        throws NoSuchMethodException, IllegalAccessException {
      if (refc == MethodHandle.class) {
        MethodHandle mh = findVirtualForMH(name, type);
        if (mh != null) {
          return mh;
        }
      }
      byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
      MemberName method = resolveOrFail(refKind, refc, name, type);
      return getDirectMethod(refKind, refc, method, findBoundCallerClass(method));
    }

    private MethodHandle findVirtualForMH(String name, MethodType type) {
      // these names require special lookups because of the implicit MethodType argument
      if ("invoke".equals(name)) {
        return invoker(type);
      }
      if ("invokeExact".equals(name)) {
        return exactInvoker(type);
      }
      if ("invokeBasic".equals(name)) {
        return basicInvoker(type);
      }
      assert (!MemberName.isMethodHandleInvokeName(name));
      return null;
    }

    /**
     * Produces a method handle which creates an object and initializes it, using
     * the constructor of the specified type.
     * The parameter types of the method handle will be those of the constructor,
     * while the return type will be a reference to the constructor's class.
     * The constructor and all its argument types must be accessible to the lookup object.
     * <p>
     * The requested type must have a return type of {@code void}.
     * (This is consistent with the JVM's treatment of constructor type descriptors.)
     * <p>
     * The returned method handle will have
     * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
     * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
     * <p>
     * If the returned method handle is invoked, the constructor's class will
     * be initialized, if it has not already been initialized.
     * <p><b>Example:</b>
     * <blockquote><pre>{@code
     * import static java.lang.invoke.MethodHandles.*;
     * import static java.lang.invoke.MethodType.*;
     * ...
     * MethodHandle MH_newArrayList = publicLookup().findConstructor(
     * ArrayList.class, methodType(void.class, Collection.class));
     * Collection orig = Arrays.asList("x", "y");
     * Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
     * assert(orig != copy);
     * assertEquals(orig, copy);
     * // a variable-arity constructor:
     * MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
     * ProcessBuilder.class, methodType(void.class, String[].class));
     * ProcessBuilder pb = (ProcessBuilder)
     * MH_newProcessBuilder.invoke("x", "y", "z");
     * assertEquals("[x, y, z]", pb.command().toString());
     * }</pre></blockquote>
     *
     * @param refc the class or interface from which the method is accessed
     * @param type the type of the method, with the receiver argument omitted, and a void return
     * type
     * @return the desired method handle
     * @throws NoSuchMethodException if the constructor does not exist
     * @throws IllegalAccessException if access checking fails or if the method's variable arity
     * modifier bit is set and {@code asVarargsCollector} fails
     * @throws SecurityException if a security manager is present and it <a
     * href="MethodHandles.Lookup.html#secmgr">refuses access</a>
     * @throws NullPointerException if any argument is null
     */
    public MethodHandle findConstructor(Class<?> refc, MethodType type)
        throws NoSuchMethodException, IllegalAccessException {
      String name = "<init>";
      MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
      return getDirectConstructor(refc, ctor);
    }

    /**
     * Produces an early-bound method handle for a virtual method.
     * It will bypass checks for overriding methods on the receiver,
     * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
     * instruction from within the explicitly specified {@code specialCaller}.
     * The type of the method handle will be that of the method,
     * with a suitably restricted receiver type prepended.
     * (The receiver type will be {@code specialCaller} or a subtype.)
     * The method and all its argument types must be accessible
     * to the lookup object.
     * <p>
     * Before method resolution,
     * if the explicitly specified caller class is not identical with the
     * lookup class, or if this lookup object does not have
     * <a href="MethodHandles.Lookup.html#privacc">private access</a>
     * privileges, the access fails.
     * <p>
     * The returned method handle will have
     * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
     * the method's variable arity modifier bit ({@code 0x0080}) is set.
     * <p style="font-size:smaller;">
     * <em>(Note:  JVM internal methods named {@code "<init>"} are not visible to this API,
     * even though the {@code invokespecial} instruction can refer to them
     * in special circumstances.  Use {@link #findConstructor findConstructor}
     * to access instance initialization methods in a safe manner.)</em>
     * <p><b>Example:</b>
     * <blockquote><pre>{@code
     * import static java.lang.invoke.MethodHandles.*;
     * import static java.lang.invoke.MethodType.*;
     * ...
     * static class Listie extends ArrayList {
     * public String toString() { return "[wee Listie]"; }
     * static Lookup lookup() { return MethodHandles.lookup(); }
     * }
     * ...
     * // no access to constructor via invokeSpecial:
     * MethodHandle MH_newListie = Listie.lookup()
     * .findConstructor(Listie.class, methodType(void.class));
     * Listie l = (Listie) MH_newListie.invokeExact();
     * try { assertEquals("impossible", Listie.lookup().findSpecial(
     * Listie.class, "<init>", methodType(void.class), Listie.class));
     * } catch (NoSuchMethodException ex) { } // OK
     * // access to super and self methods via invokeSpecial:
     * MethodHandle MH_super = Listie.lookup().findSpecial(
     * ArrayList.class, "toString" , methodType(String.class), Listie.class);
     * MethodHandle MH_this = Listie.lookup().findSpecial(
     * Listie.class, "toString" , methodType(String.class), Listie.class);
     * MethodHandle MH_duper = Listie.lookup().findSpecial(
     * Object.class, "toString" , methodType(String.class), Listie.class);
     * assertEquals("[]", (String) MH_super.invokeExact(l));
     * assertEquals(""+l, (String) MH_this.invokeExact(l));
     * assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
     * try { assertEquals("inaccessible", Listie.lookup().findSpecial(
     * String.class, "toString", methodType(String.class), Listie.class));
     * } catch (IllegalAccessException ex) { } // OK
     * Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
     * assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
     * }</pre></blockquote>
     *
     * @param refc the class or interface from which the method is accessed
     * @param name the name of the method (which must not be "&lt;init&gt;")
     * @param type the type of the method, with the receiver argument omitted
     * @param specialCaller the proposed calling class to perform the {@code invokespecial}
     * @return the desired method handle
     * @throws NoSuchMethodException if the method does not exist
     * @throws IllegalAccessException if access checking fails or if the method's variable arity
     * modifier bit is set and {@code asVarargsCollector} fails
     * @throws SecurityException if a security manager is present and it <a
     * href="MethodHandles.Lookup.html#secmgr">refuses access</a>
     * @throws NullPointerException if any argument is null
     */
    public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
        Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
      checkSpecialCaller(specialCaller);
      Lookup specialLookup = this.in(specialCaller);
      MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
      return specialLookup
          .getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
    }

    /**
     * Produces a method handle giving read access to a non-static field.
     * The type of the method handle will have a return type of the field's
     * value type.
     * The method handle's single argument will be the instance containing
     * the field.
     * Access checking is performed immediately on behalf of the lookup class.
     *
     * @param refc the class or interface from which the method is accessed
     * @param name the field's name
     * @param type the field's type
     * @return a method handle which can load values from the field
     * @throws NoSuchFieldException if the field does not exist
     * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
     * @throws SecurityException if a security manager is present and it <a
     * href="MethodHandles.Lookup.html#secmgr">refuses access</a>
     * @throws NullPointerException if any argument is null
     */
    public MethodHandle findGetter(Class<?> refc, String name, Class<?> type)
        throws NoSuchFieldException, IllegalAccessException {
      MemberName field = resolveOrFail(REF_getField, refc, name, type);
      return getDirectField(REF_getField, refc, field);
    }

    /**
     * Produces a method handle giving write access to a non-static field.
     * The type of the method handle will have a void return type.
     * The method handle will take two arguments, the instance containing
     * the field, and the value to be stored.
     * The second argument will be of the field's value type.
     * Access checking is performed immediately on behalf of the lookup class.
     *
     * @param refc the class or interface from which the method is accessed
     * @param name the field's name
     * @param type the field's type
     * @return a method handle which can store values into the field
     * @throws NoSuchFieldException if the field does not exist
     * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
     * @throws SecurityException if a security manager is present and it <a
     * href="MethodHandles.Lookup.html#secmgr">refuses access</a>
     * @throws NullPointerException if any argument is null
     */
    public MethodHandle findSetter(Class<?> refc, String name, Class<?> type)
        throws NoSuchFieldException, IllegalAccessException {
      MemberName field = resolveOrFail(REF_putField, refc, name, type);
      return getDirectField(REF_putField, refc, field);
    }

    /**
     * Produces a method handle giving read access to a static field.
     * The type of the method handle will have a return type of the field's
     * value type.
     * The method handle will take no arguments.
     * Access checking is performed immediately on behalf of the lookup class.
     * <p>
     * If the returned method handle is invoked, the field's class will
     * be initialized, if it has not already been initialized.
     *
     * @param refc the class or interface from which the method is accessed
     * @param name the field's name
     * @param type the field's type
     * @return a method handle which can load values from the field
     * @throws NoSuchFieldException if the field does not exist
     * @throws IllegalAccessException if access checking fails, or if the field is not {@code
     * static}
     * @throws SecurityException if a security manager is present and it <a
     * href="MethodHandles.Lookup.html#secmgr">refuses access</a>
     * @throws NullPointerException if any argument is null
     */
    public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type)
        throws NoSuchFieldException, IllegalAccessException {
      MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
      return getDirectField(REF_getStatic, refc, field);
    }

    /**
     * Produces a method handle giving write access to a static field.
     * The type of the method handle will have a void return type.
     * The method handle will take a single
     * argument, of the field's value type, the value to be stored.
     * Access checking is performed immediately on behalf of the lookup class.
     * <p>
     * If the returned method handle is invoked, the field's class will
     * be initialized, if it has not already been initialized.
     *
     * @param refc the class or interface from which the method is accessed
     * @param name the field's name
     * @param type the field's type
     * @return a method handle which can store values into the field
     * @throws NoSuchFieldException if the field does not exist
     * @throws IllegalAccessException if access checking fails, or if the field is not {@code
     * static}
     * @throws SecurityException if a security manager is present and it <a
     * href="MethodHandles.Lookup.html#secmgr">refuses access</a>
     * @throws NullPointerException if any argument is null
     */
    public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type)
        throws NoSuchFieldException, IllegalAccessException {
      MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
      return getDirectField(REF_putStatic, refc, field);
    }

    /**
     * Produces an early-bound method handle for a non-static method.
     * The receiver must have a supertype {@code defc} in which a method
     * of the given name and type is accessible to the lookup class.
     * The method and all its argument types must be accessible to the lookup object.
     * The type of the method handle will be that of the method,
     * without any insertion of an additional receiver parameter.
     * The given receiver will be bound into the method handle,
     * so that every call to the method handle will invoke the
     * requested method on the given receiver.
     * <p>
     * The returned method handle will have
     * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
     * the method's variable arity modifier bit ({@code 0x0080}) is set
     * <em>and</em> the trailing array argument is not the only argument.
     * (If the trailing array argument is the only argument,
     * the given receiver value will be bound to it.)
     * <p>
     * This is equivalent to the following code:
     * <blockquote><pre>{@code
     * import static java.lang.invoke.MethodHandles.*;
     * import static java.lang.invoke.MethodType.*;
     * ...
     * MethodHandle mh0 = lookup().findVirtual(defc, name, type);
     * MethodHandle mh1 = mh0.bindTo(receiver);
     * MethodType mt1 = mh1.type();
     * if (mh0.isVarargsCollector())
     * mh1 = mh1.asVarargsCollector(mt1.parameterType(mt1.parameterCount()-1));
     * return mh1;
     * }</pre></blockquote>
     * where {@code defc} is either {@code receiver.getClass()} or a super
     * type of that class, in which the requested method is accessible
     * to the lookup class.
     * (Note that {@code bindTo} does not preserve variable arity.)
     *
     * @param receiver the object from which the method is accessed
     * @param name the name of the method
     * @param type the type of the method, with the receiver argument omitted
     * @return the desired method handle
     * @throws NoSuchMethodException if the method does not exist
     * @throws IllegalAccessException if access checking fails or if the method's variable arity
     * modifier bit is set and {@code asVarargsCollector} fails
     * @throws SecurityException if a security manager is present and it <a
     * href="MethodHandles.Lookup.html#secmgr">refuses access</a>
     * @throws NullPointerException if any argument is null
     * @see MethodHandle#bindTo
     * @see #findVirtual
     */
    public MethodHandle bind(Object receiver, String name, MethodType type)
        throws NoSuchMethodException, IllegalAccessException {
      Class<? extends Object> refc = receiver.getClass(); // may get NPE
      MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
      MethodHandle mh = getDirectMethodNoRestrict(REF_invokeSpecial, refc, method,
          findBoundCallerClass(method));
      return mh.bindArgumentL(0, receiver).setVarargs(method);
    }

    /**
     * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
     * to <i>m</i>, if the lookup class has permission.
     * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
     * If <i>m</i> is virtual, overriding is respected on every call.
     * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
     * The type of the method handle will be that of the method,
     * with the receiver type prepended (but only if it is non-static).
     * If the method's {@code accessible} flag is not set,
     * access checking is performed immediately on behalf of the lookup class.
     * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
     * <p>
     * The returned method handle will have
     * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
     * the method's variable arity modifier bit ({@code 0x0080}) is set.
     * <p>
     * If <i>m</i> is static, and
     * if the returned method handle is invoked, the method's class will
     * be initialized, if it has not already been initialized.
     *
     * @param m the reflected method
     * @return a method handle which can invoke the reflected method
     * @throws IllegalAccessException if access checking fails or if the method's variable arity
     * modifier bit is set and {@code asVarargsCollector} fails
     * @throws NullPointerException if the argument is null
     */
    public MethodHandle unreflect(Method m) throws IllegalAccessException {
      if (m.getDeclaringClass() == MethodHandle.class) {
        MethodHandle mh = unreflectForMH(m);
        if (mh != null) {
          return mh;
        }
      }
      MemberName method = new MemberName(m);
      byte refKind = method.getReferenceKind();
      if (refKind == REF_invokeSpecial) {
        refKind = REF_invokeVirtual;
      }
      assert (method.isMethod());
      Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
      return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method,
          findBoundCallerClass(method));
    }

    private MethodHandle unreflectForMH(Method m) {
      // these names require special lookups because they throw UnsupportedOperationException
      if (MemberName.isMethodHandleInvokeName(m.getName())) {
        return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
      }
      return null;
    }

    /**
     * Produces a method handle for a reflected method.
     * It will bypass checks for overriding methods on the receiver,
     * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
     * instruction from within the explicitly specified {@code specialCaller}.
     * The type of the method handle will be that of the method,
     * with a suitably restricted receiver type prepended.
     * (The receiver type will be {@code specialCaller} or a subtype.)
     * If the method's {@code accessible} flag is not set,
     * access checking is performed immediately on behalf of the lookup class,
     * as if {@code invokespecial} instruction were being linked.
     * <p>
     * Before method resolution,
     * if the explicitly specified caller class is not identical with the
     * lookup class, or if this lookup object does not have
     * <a href="MethodHandles.Lookup.html#privacc">private access</a>
     * privileges, the access fails.
     * <p>
     * The returned method handle will have
     * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
     * the method's variable arity modifier bit ({@code 0x0080}) is set.
     *
     * @param m the reflected method
     * @param specialCaller the class nominally calling the method
     * @return a method handle which can invoke the reflected method
     * @throws IllegalAccessException if access checking fails or if the method's variable arity
     * modifier bit is set and {@code asVarargsCollector} fails
     * @throws NullPointerException if any argument is null
     */
    public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller)
        throws IllegalAccessException {
      checkSpecialCaller(specialCaller);
      Lookup specialLookup = this.in(specialCaller);
      MemberName method = new MemberName(m, true);
      assert (method.isMethod());
      // ignore m.isAccessible:  this is a new kind of access
      return specialLookup
          .getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method,
              findBoundCallerClass(method));
    }

    /**
     * Produces a method handle for a reflected constructor.
     * The type of the method handle will be that of the constructor,
     * with the return type changed to the declaring class.
     * The method handle will perform a {@code newInstance} operation,
     * creating a new instance of the constructor's class on the
     * arguments passed to the method handle.
     * <p>
     * If the constructor's {@code accessible} flag is not set,
     * access checking is performed immediately on behalf of the lookup class.
     * <p>
     * The returned method handle will have
     * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
     * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
     * <p>
     * If the returned method handle is invoked, the constructor's class will
     * be initialized, if it has not already been initialized.
     *
     * @param c the reflected constructor
     * @return a method handle which can invoke the reflected constructor
     * @throws IllegalAccessException if access checking fails or if the method's variable arity
     * modifier bit is set and {@code asVarargsCollector} fails
     * @throws NullPointerException if the argument is null
     */
    public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
      MemberName ctor = new MemberName(c);
      assert (ctor.isConstructor());
      Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
      return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
    }

    /**
     * Produces a method handle giving read access to a reflected field.
     * The type of the method handle will have a return type of the field's
     * value type.
     * If the field is static, the method handle will take no arguments.
     * Otherwise, its single argument will be the instance containing
     * the field.
     * If the field's {@code accessible} flag is not set,
     * access checking is performed immediately on behalf of the lookup class.
     * <p>
     * If the field is static, and
     * if the returned method handle is invoked, the field's class will
     * be initialized, if it has not already been initialized.
     *
     * @param f the reflected field
     * @return a method handle which can load values from the reflected field
     * @throws IllegalAccessException if access checking fails
     * @throws NullPointerException if the argument is null
     */
    public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
      return unreflectField(f, false);
    }

    private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
      MemberName field = new MemberName(f, isSetter);
      assert (isSetter
          ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
          : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
      Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
      return lookup
          .getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
    }

    /**
     * Produces a method handle giving write access to a reflected field.
     * The type of the method handle will have a void return type.
     * If the field is static, the method handle will take a single
     * argument, of the field's value type, the value to be stored.
     * Otherwise, the two arguments will be the instance containing
     * the field, and the value to be stored.
     * If the field's {@code accessible} flag is not set,
     * access checking is performed immediately on behalf of the lookup class.
     * <p>
     * If the field is static, and
     * if the returned method handle is invoked, the field's class will
     * be initialized, if it has not already been initialized.
     *
     * @param f the reflected field
     * @return a method handle which can store values into the reflected field
     * @throws IllegalAccessException if access checking fails
     * @throws NullPointerException if the argument is null
     */
    public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
      return unreflectField(f, true);
    }

    /**
     * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a> created by this
     * lookup object or a similar one. Security and access checks are performed to ensure that this
     * lookup object is capable of reproducing the target method handle. This means that the
     * cracking may fail if target is a direct method handle but was created by an unrelated lookup
     * object. This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller
     * sensitive</a> and was created by a lookup object for a different class.
     *
     * @param target a direct method handle to crack into symbolic reference components
     * @return a symbolic reference which can be used to reconstruct this method handle from this
     * lookup object
     * @throws SecurityException if a security manager is present and it <a
     * href="MethodHandles.Lookup.html#secmgr">refuses access</a>
     * @throws IllegalArgumentException if the target is not a direct method handle or if access
     * checking fails
     * @throws NullPointerException if the target is {@code null}
     * @see MethodHandleInfo
     * @since 1.8
     */
    public MethodHandleInfo revealDirect(MethodHandle target) {
      MemberName member = target.internalMemberName();
      if (member == null || (!member.isResolved() && !member.isMethodHandleInvoke())) {
        throw newIllegalArgumentException("not a direct method handle");
      }
      Class<?> defc = member.getDeclaringClass();
      byte refKind = member.getReferenceKind();
      assert (MethodHandleNatives.refKindIsValid(refKind));
      if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
      // Devirtualized method invocation is usually formally virtual.
      // To avoid creating extra MemberName objects for this common case,
      // we encode this extra degree of freedom using MH.isInvokeSpecial.
      {
        refKind = REF_invokeVirtual;
      }
      if (refKind == REF_invokeVirtual && defc.isInterface())
      // Symbolic reference is through interface but resolves to Object method (toString, etc.)
      {
        refKind = REF_invokeInterface;
      }
      // Check SM permissions and member access before cracking.
      try {
        checkAccess(refKind, defc, member);
        checkSecurityManager(defc, member);
      } catch (IllegalAccessException ex) {
        throw new IllegalArgumentException(ex);
      }
      if (allowedModes != TRUSTED && member.isCallerSensitive()) {
        Class<?> callerClass = target.internalCallerClass();
        if (!hasPrivateAccess() || callerClass != lookupClass()) {
          throw new IllegalArgumentException("method handle is caller sensitive: " + callerClass);
        }
      }
      // Produce the handle to the results.
      return new InfoFromMemberName(this, member, refKind);
    }

    /// Helper methods, all package-private.

    MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type)
        throws NoSuchFieldException, IllegalAccessException {
      checkSymbolicClass(refc);  // do this before attempting to resolve
      name.getClass();  // NPE
      type.getClass();  // NPE
      return IMPL_NAMES
          .resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
              NoSuchFieldException.class);
    }

    MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type)
        throws NoSuchMethodException, IllegalAccessException {
      checkSymbolicClass(refc);  // do this before attempting to resolve
      name.getClass();  // NPE
      type.getClass();  // NPE
      checkMethodName(refKind, name);  // NPE check on name
      return IMPL_NAMES
          .resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
              NoSuchMethodException.class);
    }

    MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
      checkSymbolicClass(member.getDeclaringClass());  // do this before attempting to resolve
      member.getName().getClass();  // NPE
      member.getType().getClass();  // NPE
      return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(),
          ReflectiveOperationException.class);
    }

    void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
      refc.getClass();  // NPE
      Class<?> caller = lookupClassOrNull();
      if (caller != null && !VerifyAccess.isClassAccessible(refc, caller, allowedModes)) {
        throw new MemberName(refc)
            .makeAccessException("symbolic reference class is not public", this);
      }
    }

    /**
     * Check name for an illegal leading "&lt;" character.
     */
    void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
      if (name.startsWith("<") && refKind != REF_newInvokeSpecial) {
        throw new NoSuchMethodException("illegal method name: " + name);
      }
    }


    /**
     * Find my trustable caller class if m is a caller sensitive method.
     * If this lookup object has private access, then the caller class is the lookupClass.
     * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
     */
    Class<?> findBoundCallerClass(MemberName m) throws IllegalAccessException {
      Class<?> callerClass = null;
      if (MethodHandleNatives.isCallerSensitive(m)) {
        // Only lookups with private access are allowed to resolve caller-sensitive methods
        if (hasPrivateAccess()) {
          callerClass = lookupClass;
        } else {
          throw new IllegalAccessException(
              "Attempt to lookup caller-sensitive method using restricted lookup object");
        }
      }
      return callerClass;
    }

    private boolean hasPrivateAccess() {
      return (allowedModes & PRIVATE) != 0;
    }

    /**
     * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
     * Determines a trustable caller class to compare with refc, the symbolic reference class.
     * If this lookup object has private access, then the caller class is the lookupClass.
     */
    void checkSecurityManager(Class<?> refc, MemberName m) {
      SecurityManager smgr = System.getSecurityManager();
      if (smgr == null) {
        return;
      }
      if (allowedModes == TRUSTED) {
        return;
      }

      // Step 1:
      boolean fullPowerLookup = hasPrivateAccess();
      if (!fullPowerLookup ||
          !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
        ReflectUtil.checkPackageAccess(refc);
      }

      // Step 2:
      if (m.isPublic()) {
        return;
      }
      if (!fullPowerLookup) {
        smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
      }

      // Step 3:
      Class<?> defc = m.getDeclaringClass();
      if (!fullPowerLookup && defc != refc) {
        ReflectUtil.checkPackageAccess(defc);
      }
    }

    void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
      boolean wantStatic = (refKind == REF_invokeStatic);
      String message;
      if (m.isConstructor()) {
        message = "expected a method, not a constructor";
      } else if (!m.isMethod()) {
        message = "expected a method";
      } else if (wantStatic != m.isStatic()) {
        message = wantStatic ? "expected a static method" : "expected a non-static method";
      } else {
        checkAccess(refKind, refc, m);
        return;
      }
      throw m.makeAccessException(message, this);
    }

    void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
      boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
      String message;
      if (wantStatic != m.isStatic()) {
        message = wantStatic ? "expected a static field" : "expected a non-static field";
      } else {
        checkAccess(refKind, refc, m);
        return;
      }
      throw m.makeAccessException(message, this);
    }

    /**
     * Check public/protected/private bits on the symbolic reference class and its member.
     */
    void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
      assert (m.referenceKindIsConsistentWith(refKind) &&
          MethodHandleNatives.refKindIsValid(refKind) &&
          (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
      int allowedModes = this.allowedModes;
      if (allowedModes == TRUSTED) {
        return;
      }
      int mods = m.getModifiers();
      if (Modifier.isProtected(mods) &&
          refKind == REF_invokeVirtual &&
          m.getDeclaringClass() == Object.class &&
          m.getName().equals("clone") &&
          refc.isArray()) {
        // The JVM does this hack also.
        // (See ClassVerifier::verify_invoke_instructions
        // and LinkResolver::check_method_accessability.)
        // Because the JVM does not allow separate methods on array types,
        // there is no separate method for int[].clone.
        // All arrays simply inherit Object.clone.
        // But for access checking logic, we make Object.clone
        // (normally protected) appear to be public.
        // Later on, when the DirectMethodHandle is created,
        // its leading argument will be restricted to the
        // requested array type.
        // N.B. The return type is not adjusted, because
        // that is *not* the bytecode behavior.
        mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
      }
      if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
        // cannot "new" a protected ctor in a different package
        mods ^= Modifier.PROTECTED;
      }
      if (Modifier.isFinal(mods) &&
          MethodHandleNatives.refKindIsSetter(refKind)) {
        throw m.makeAccessException("unexpected set of a final field", this);
      }
      if (Modifier.isPublic(mods) && Modifier.isPublic(refc.getModifiers()) && allowedModes != 0) {
        return;  // common case
      }
      int requestedModes = fixmods(mods);  // adjust 0 => PACKAGE
      if ((requestedModes & allowedModes) != 0) {
        if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
            mods, lookupClass(), allowedModes)) {
          return;
        }
      } else {
        // Protected members can also be checked as if they were package-private.
        if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
            && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass())) {
          return;
        }
      }
      throw m.makeAccessException(accessFailedMessage(refc, m), this);
    }

    String accessFailedMessage(Class<?> refc, MemberName m) {
      Class<?> defc = m.getDeclaringClass();
      int mods = m.getModifiers();
      // check the class first:
      boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
          (defc == refc ||
              Modifier.isPublic(refc.getModifiers())));
      if (!classOK && (allowedModes & PACKAGE) != 0) {
        classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), ALL_MODES) &&
            (defc == refc ||
                VerifyAccess.isClassAccessible(refc, lookupClass(), ALL_MODES)));
      }
      if (!classOK) {
        return "class is not public";
      }
      if (Modifier.isPublic(mods)) {
        return "access to public member failed";  // (how?)
      }
      if (Modifier.isPrivate(mods)) {
        return "member is private";
      }
      if (Modifier.isProtected(mods)) {
        return "member is protected";
      }
      return "member is private to package";
    }

    private static final boolean ALLOW_NESTMATE_ACCESS = false;

    private void checkSpecialCaller(Class<?> specialCaller) throws IllegalAccessException {
      int allowedModes = this.allowedModes;
      if (allowedModes == TRUSTED) {
        return;
      }
      if (!hasPrivateAccess()
          || (specialCaller != lookupClass()
          && !(ALLOW_NESTMATE_ACCESS &&
          VerifyAccess.isSamePackageMember(specialCaller, lookupClass())))) {
        throw new MemberName(specialCaller).
            makeAccessException("no private access for invokespecial", this);
      }
    }

    private boolean restrictProtectedReceiver(MemberName method) {
      // The accessing class only has the right to use a protected member
      // on itself or a subclass.  Enforce that restriction, from JVMS 5.4.4, etc.
      if (!method.isProtected() || method.isStatic()
          || allowedModes == TRUSTED
          || method.getDeclaringClass() == lookupClass()
          || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass())
          || (ALLOW_NESTMATE_ACCESS &&
          VerifyAccess.isSamePackageMember(method.getDeclaringClass(), lookupClass()))) {
        return false;
      }
      return true;
    }

    private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller)
        throws IllegalAccessException {
      assert (!method.isStatic());
      // receiver type of mh is too wide; narrow to caller
      if (!method.getDeclaringClass().isAssignableFrom(caller)) {
        throw method
            .makeAccessException("caller class must be a subclass below the method", caller);
      }
      MethodType rawType = mh.type();
      if (rawType.parameterType(0) == caller) {
        return mh;
      }
      MethodType narrowType = rawType.changeParameterType(0, caller);
      assert (!mh.isVarargsCollector());  // viewAsType will lose varargs-ness
      assert (mh.viewAsTypeChecks(narrowType, true));
      return mh.copyWith(narrowType, mh.form);
    }

    /**
     * Check access and get the requested method.
     */
    private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method,
        Class<?> callerClass) throws IllegalAccessException {
      final boolean doRestrict = true;
      final boolean checkSecurity = true;
      return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
    }

    /**
     * Check access and get the requested method, eliding receiver narrowing rules.
     */
    private MethodHandle getDirectMethodNoRestrict(byte refKind, Class<?> refc, MemberName method,
        Class<?> callerClass) throws IllegalAccessException {
      final boolean doRestrict = false;
      final boolean checkSecurity = true;
      return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
    }

    /**
     * Check access and get the requested method, eliding security manager checks.
     */
    private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc,
        MemberName method, Class<?> callerClass) throws IllegalAccessException {
      final boolean doRestrict = true;
      final boolean checkSecurity = false;  // not needed for reflection or for linking CONSTANT_MH constants
      return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
    }

    /**
     * Common code for all methods; do not call directly except from immediately above.
     */
    private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
        boolean checkSecurity,
        boolean doRestrict, Class<?> callerClass) throws IllegalAccessException {
      checkMethod(refKind, refc, method);
      // Optionally check with the security manager; this isn't needed for unreflect* calls.
      if (checkSecurity) {
        checkSecurityManager(refc, method);
      }
      assert (!method.isMethodHandleInvoke());

      if (refKind == REF_invokeSpecial &&
          refc != lookupClass() &&
          !refc.isInterface() &&
          refc != lookupClass().getSuperclass() &&
          refc.isAssignableFrom(lookupClass())) {
        assert (!method.getName().equals("<init>"));  // not this code path
        // Per JVMS 6.5, desc. of invokespecial instruction:
        // If the method is in a superclass of the LC,
        // and if our original search was above LC.super,
        // repeat the search (symbolic lookup) from LC.super
        // and continue with the direct superclass of that class,
        // and so forth, until a match is found or no further superclasses exist.
        // FIXME: MemberName.resolve should handle this instead.
        Class<?> refcAsSuper = lookupClass();
        MemberName m2;
        do {
          refcAsSuper = refcAsSuper.getSuperclass();
          m2 = new MemberName(refcAsSuper,
              method.getName(),
              method.getMethodType(),
              REF_invokeSpecial);
          m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull());
        } while (m2 == null &&         // no method is found yet
            refc != refcAsSuper); // search up to refc
        if (m2 == null) {
          throw new InternalError(method.toString());
        }
        method = m2;
        refc = refcAsSuper;
        // redo basic checks
        checkMethod(refKind, refc, method);
      }

      DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method);
      MethodHandle mh = dmh;
      // Optionally narrow the receiver argument to refc using restrictReceiver.
      if (doRestrict &&
          (refKind == REF_invokeSpecial ||
              (MethodHandleNatives.refKindHasReceiver(refKind) &&
                  restrictProtectedReceiver(method)))) {
        mh = restrictReceiver(method, dmh, lookupClass());
      }
      mh = maybeBindCaller(method, mh, callerClass);
      mh = mh.setVarargs(method);
      return mh;
    }

    private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh,
        Class<?> callerClass)
        throws IllegalAccessException {
      if (allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method)) {
        return mh;
      }
      Class<?> hostClass = lookupClass;
      if (!hasPrivateAccess())  // caller must have private access
      {
        hostClass = callerClass;  // callerClass came from a security manager style stack walk
      }
      MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, hostClass);
      // Note: caller will apply varargs after this step happens.
      return cbmh;
    }

    /**
     * Check access and get the requested field.
     */
    private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field)
        throws IllegalAccessException {
      final boolean checkSecurity = true;
      return getDirectFieldCommon(refKind, refc, field, checkSecurity);
    }

    /**
     * Check access and get the requested field, eliding security manager checks.
     */
    private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc,
        MemberName field) throws IllegalAccessException {
      final boolean checkSecurity = false;  // not needed for reflection or for linking CONSTANT_MH constants
      return getDirectFieldCommon(refKind, refc, field, checkSecurity);
    }

    /**
     * Common code for all fields; do not call directly except from immediately above.
     */
    private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
        boolean checkSecurity) throws IllegalAccessException {
      checkField(refKind, refc, field);
      // Optionally check with the security manager; this isn't needed for unreflect* calls.
      if (checkSecurity) {
        checkSecurityManager(refc, field);
      }
      DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
      boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
          restrictProtectedReceiver(field));
      if (doRestrict) {
        return restrictReceiver(field, dmh, lookupClass());
      }
      return dmh;
    }

    /**
     * Check access and get the requested constructor.
     */
    private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor)
        throws IllegalAccessException {
      final boolean checkSecurity = true;
      return getDirectConstructorCommon(refc, ctor, checkSecurity);
    }

    /**
     * Check access and get the requested constructor, eliding security manager checks.
     */
    private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor)
        throws IllegalAccessException {
      final boolean checkSecurity = false;  // not needed for reflection or for linking CONSTANT_MH constants
      return getDirectConstructorCommon(refc, ctor, checkSecurity);
    }

    /**
     * Common code for all constructors; do not call directly except from immediately above.
     */
    private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
        boolean checkSecurity) throws IllegalAccessException {
      assert (ctor.isConstructor());
      checkAccess(REF_newInvokeSpecial, refc, ctor);
      // Optionally check with the security manager; this isn't needed for unreflect* calls.
      if (checkSecurity) {
        checkSecurityManager(refc, ctor);
      }
      assert (!MethodHandleNatives.isCallerSensitive(ctor));  // maybeBindCaller not relevant here
      return DirectMethodHandle.make(ctor).setVarargs(ctor);
    }

    /**
     * Hook called from the JVM (via MethodHandleNatives) to link MH constants:
     */
        /*non-public*/
    MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type)
        throws ReflectiveOperationException {
      if (!(type instanceof Class || type instanceof MethodType)) {
        throw new InternalError("unresolved MemberName");
      }
      MemberName member = new MemberName(refKind, defc, name, type);
      MethodHandle mh = LOOKASIDE_TABLE.get(member);
      if (mh != null) {
        checkSymbolicClass(defc);
        return mh;
      }
      // Treat MethodHandle.invoke and invokeExact specially.
      if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
        mh = findVirtualForMH(member.getName(), member.getMethodType());
        if (mh != null) {
          return mh;
        }
      }
      MemberName resolved = resolveOrFail(refKind, member);
      mh = getDirectMethodForConstant(refKind, defc, resolved);
      if (mh instanceof DirectMethodHandle
          && canBeCached(refKind, defc, resolved)) {
        MemberName key = mh.internalMemberName();
        if (key != null) {
          key = key.asNormalOriginal();
        }
        if (member.equals(key)) {  // better safe than sorry
          LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh);
        }
      }
      return mh;
    }

    private boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
      if (refKind == REF_invokeSpecial) {
        return false;
      }
      if (!Modifier.isPublic(defc.getModifiers()) ||
          !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
          !member.isPublic() ||
          member.isCallerSensitive()) {
        return false;
      }
      ClassLoader loader = defc.getClassLoader();
      if (!sun.misc.VM.isSystemDomainLoader(loader)) {
        ClassLoader sysl = ClassLoader.getSystemClassLoader();
        boolean found = false;
        while (sysl != null) {
          if (loader == sysl) {
            found = true;
            break;
          }
          sysl = sysl.getParent();
        }
        if (!found) {
          return false;
        }
      }
      try {
        MemberName resolved2 = publicLookup().resolveOrFail(refKind,
            new MemberName(refKind, defc, member.getName(), member.getType()));
        checkSecurityManager(defc, resolved2);
      } catch (ReflectiveOperationException | SecurityException ex) {
        return false;
      }
      return true;
    }

    private MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
        throws ReflectiveOperationException {
      if (MethodHandleNatives.refKindIsField(refKind)) {
        return getDirectFieldNoSecurityManager(refKind, defc, member);
      } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
        return getDirectMethodNoSecurityManager(refKind, defc, member, lookupClass);
      } else if (refKind == REF_newInvokeSpecial) {
        return getDirectConstructorNoSecurityManager(defc, member);
      }
      // oops
      throw newIllegalArgumentException("bad MethodHandle constant #" + member);
    }

    static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
  }

  /**
   * Produces a method handle giving read access to elements of an array.
   * The type of the method handle will have a return type of the array's
   * element type.  Its first argument will be the array type,
   * and the second will be {@code int}.
   *
   * @param arrayClass an array type
   * @return a method handle which can load values from the given array type
   * @throws NullPointerException if the argument is null
   * @throws IllegalArgumentException if arrayClass is not an array type
   */
  public static MethodHandle arrayElementGetter(Class<?> arrayClass)
      throws IllegalArgumentException {
    return MethodHandleImpl.makeArrayElementAccessor(arrayClass, false);
  }

  /**
   * Produces a method handle giving write access to elements of an array.
   * The type of the method handle will have a void return type.
   * Its last argument will be the array's element type.
   * The first and second arguments will be the array type and int.
   *
   * @param arrayClass the class of an array
   * @return a method handle which can store values into the array type
   * @throws NullPointerException if the argument is null
   * @throws IllegalArgumentException if arrayClass is not an array type
   */
  public static MethodHandle arrayElementSetter(Class<?> arrayClass)
      throws IllegalArgumentException {
    return MethodHandleImpl.makeArrayElementAccessor(arrayClass, true);
  }

  /// method handle invocation (reflective style)

  /**
   * Produces a method handle which will invoke any method handle of the
   * given {@code type}, with a given number of trailing arguments replaced by
   * a single trailing {@code Object[]} array.
   * The resulting invoker will be a method handle with the following
   * arguments:
   * <ul>
   * <li>a single {@code MethodHandle} target
   * <li>zero or more leading values (counted by {@code leadingArgCount})
   * <li>an {@code Object[]} array containing trailing arguments
   * </ul>
   * <p>
   * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
   * the indicated {@code type}.
   * That is, if the target is exactly of the given {@code type}, it will behave
   * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
   * is used to convert the target to the required {@code type}.
   * <p>
   * The type of the returned invoker will not be the given {@code type}, but rather
   * will have all parameters except the first {@code leadingArgCount}
   * replaced by a single array of type {@code Object[]}, which will be
   * the final parameter.
   * <p>
   * Before invoking its target, the invoker will spread the final array, apply
   * reference casts as necessary, and unbox and widen primitive arguments.
   * If, when the invoker is called, the supplied array argument does
   * not have the correct number of elements, the invoker will throw
   * an {@link IllegalArgumentException} instead of invoking the target.
   * <p>
   * This method is equivalent to the following code (though it may be more efficient):
   * <blockquote><pre>{@code
   * MethodHandle invoker = MethodHandles.invoker(type);
   * int spreadArgCount = type.parameterCount() - leadingArgCount;
   * invoker = invoker.asSpreader(Object[].class, spreadArgCount);
   * return invoker;
   * }</pre></blockquote>
   * This method throws no reflective or security exceptions.
   *
   * @param type the desired target type
   * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
   * @return a method handle suitable for invoking any method handle of the given type
   * @throws NullPointerException if {@code type} is null
   * @throws IllegalArgumentException if {@code leadingArgCount} is not in the range from 0 to
   * {@code type.parameterCount()} inclusive, or if the resulting method handle's type would have <a
   * href="MethodHandle.html#maxarity">too many parameters</a>
   */
  static public MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
    if (leadingArgCount < 0 || leadingArgCount > type.parameterCount()) {
      throw newIllegalArgumentException("bad argument count", leadingArgCount);
    }
    type = type.asSpreaderType(Object[].class, type.parameterCount() - leadingArgCount);
    return type.invokers().spreadInvoker(leadingArgCount);
  }

  /**
   * Produces a special <em>invoker method handle</em> which can be used to invoke any method handle
   * of the given type, as if by {@link MethodHandle#invokeExact invokeExact}. The resulting invoker
   * will have a type which is exactly equal to the desired type, except that it will accept an
   * additional leading argument of type {@code MethodHandle}. <p> This method is equivalent to the
   * following code (though it may be more efficient): {@code publicLookup().findVirtual(MethodHandle.class,
   * "invokeExact", type)}
   *
   * <p style="font-size:smaller;"> <em>Discussion:</em> Invoker method handles can be useful when
   * working with variable method handles of unknown types. For example, to emulate an {@code
   * invokeExact} call to a variable method handle {@code M}, extract its type {@code T}, look up
   * the invoker method {@code X} for {@code T}, and call the invoker method, as {@code X.invoke(T,
   * A...)}. (It would not work to call {@code X.invokeExact}, since the type {@code T} is unknown.)
   * If spreading, collecting, or other argument transformations are required, they can be applied
   * once to the invoker {@code X} and reused on many {@code M} method handle values, as long as
   * they are compatible with the type of {@code X}. <p style="font-size:smaller;"> <em>(Note:  The
   * invoker method is not available via the Core Reflection API. An attempt to call {@linkplain
   * java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke} on the declared {@code
   * invokeExact} or {@code invoke} method will raise an {@link java.lang.UnsupportedOperationException
   * UnsupportedOperationException}.)</em> <p> This method throws no reflective or security
   * exceptions.
   *
   * @param type the desired target type
   * @return a method handle suitable for invoking any method handle of the given type
   * @throws IllegalArgumentException if the resulting method handle's type would have <a
   * href="MethodHandle.html#maxarity">too many parameters</a>
   */
  static public MethodHandle exactInvoker(MethodType type) {
    return type.invokers().exactInvoker();
  }

  /**
   * Produces a special <em>invoker method handle</em> which can be used to invoke any method handle
   * compatible with the given type, as if by {@link MethodHandle#invoke invoke}. The resulting
   * invoker will have a type which is exactly equal to the desired type, except that it will accept
   * an additional leading argument of type {@code MethodHandle}. <p> Before invoking its target, if
   * the target differs from the expected type, the invoker will apply reference casts as necessary
   * and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
   * Similarly, the return value will be converted as necessary. If the target is a {@linkplain
   * MethodHandle#asVarargsCollector variable arity method handle}, the required arity conversion
   * will be made, again as if by {@link MethodHandle#asType asType}. <p> This method is equivalent
   * to the following code (though it may be more efficient): {@code publicLookup().findVirtual(MethodHandle.class,
   * "invoke", type)} <p style="font-size:smaller;"> <em>Discussion:</em> A {@linkplain
   * MethodType#genericMethodType general method type} is one which mentions only {@code Object}
   * arguments and return values. An invoker for such a type is capable of calling any method handle
   * of the same arity as the general type. <p style="font-size:smaller;"> <em>(Note:  The invoker
   * method is not available via the Core Reflection API. An attempt to call {@linkplain
   * java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke} on the declared {@code
   * invokeExact} or {@code invoke} method will raise an {@link java.lang.UnsupportedOperationException
   * UnsupportedOperationException}.)</em> <p> This method throws no reflective or security
   * exceptions.
   *
   * @param type the desired target type
   * @return a method handle suitable for invoking any method handle convertible to the given type
   * @throws IllegalArgumentException if the resulting method handle's type would have <a
   * href="MethodHandle.html#maxarity">too many parameters</a>
   */
  static public MethodHandle invoker(MethodType type) {
    return type.invokers().genericInvoker();
  }

  static /*non-public*/
  MethodHandle basicInvoker(MethodType type) {
    return type.invokers().basicInvoker();
  }

  /// method handle modification (creation from other method handles)

  /**
   * Produces a method handle which adapts the type of the
   * given method handle to a new type by pairwise argument and return type conversion.
   * The original type and new type must have the same number of arguments.
   * The resulting method handle is guaranteed to report a type
   * which is equal to the desired new type.
   * <p>
   * If the original type and new type are equal, returns target.
   * <p>
   * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
   * and some additional conversions are also applied if those conversions fail.
   * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
   * if possible, before or instead of any conversions done by {@code asType}:
   * <ul>
   * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
   * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
   * (This treatment of interfaces follows the usage of the bytecode verifier.)
   * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
   * the boolean is converted to a byte value, 1 for true, 0 for false.
   * (This treatment follows the usage of the bytecode verifier.)
   * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
   * <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5),
   * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
   * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
   * then a Java casting conversion (JLS 5.5) is applied.
   * (Specifically, <em>T0</em> will convert to <em>T1</em> by
   * widening and/or narrowing.)
   * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
   * conversion will be applied at runtime, possibly followed
   * by a Java casting conversion (JLS 5.5) on the primitive value,
   * possibly followed by a conversion from byte to boolean by testing
   * the low-order bit.
   * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
   * and if the reference is null at runtime, a zero value is introduced.
   * </ul>
   *
   * @param target the method handle to invoke after arguments are retyped
   * @param newType the expected type of the new method handle
   * @return a method handle which delegates to the target after performing any necessary argument
   * conversions, and arranges for any necessary return value conversions
   * @throws NullPointerException if either argument is null
   * @throws WrongMethodTypeException if the conversion cannot be made
   * @see MethodHandle#asType
   */
  public static MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
    explicitCastArgumentsChecks(target, newType);
    // use the asTypeCache when possible:
    MethodType oldType = target.type();
    if (oldType == newType) {
      return target;
    }
    if (oldType.explicitCastEquivalentToAsType(newType)) {
      return target.asFixedArity().asType(newType);
    }
    return MethodHandleImpl.makePairwiseConvert(target, newType, false);
  }

  private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
    if (target.type().parameterCount() != newType.parameterCount()) {
      throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
    }
  }

  /**
   * Produces a method handle which adapts the calling sequence of the
   * given method handle to a new type, by reordering the arguments.
   * The resulting method handle is guaranteed to report a type
   * which is equal to the desired new type.
   * <p>
   * The given array controls the reordering.
   * Call {@code #I} the number of incoming parameters (the value
   * {@code newType.parameterCount()}, and call {@code #O} the number
   * of outgoing parameters (the value {@code target.type().parameterCount()}).
   * Then the length of the reordering array must be {@code #O},
   * and each element must be a non-negative number less than {@code #I}.
   * For every {@code N} less than {@code #O}, the {@code N}-th
   * outgoing argument will be taken from the {@code I}-th incoming
   * argument, where {@code I} is {@code reorder[N]}.
   * <p>
   * No argument or return value conversions are applied.
   * The type of each incoming argument, as determined by {@code newType},
   * must be identical to the type of the corresponding outgoing parameter
   * or parameters in the target method handle.
   * The return type of {@code newType} must be identical to the return
   * type of the original target.
   * <p>
   * The reordering array need not specify an actual permutation.
   * An incoming argument will be duplicated if its index appears
   * more than once in the array, and an incoming argument will be dropped
   * if its index does not appear in the array.
   * As in the case of {@link #dropArguments(MethodHandle, int, List) dropArguments},
   * incoming arguments which are not mentioned in the reordering array
   * are may be any type, as determined only by {@code newType}.
   * <blockquote><pre>{@code
   * import static java.lang.invoke.MethodHandles.*;
   * import static java.lang.invoke.MethodType.*;
   * ...
   * MethodType intfn1 = methodType(int.class, int.class);
   * MethodType intfn2 = methodType(int.class, int.class, int.class);
   * MethodHandle sub = ... (int x, int y) -> (x-y) ...;
   * assert(sub.type().equals(intfn2));
   * MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
   * MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
   * assert((int)rsub.invokeExact(1, 100) == 99);
   * MethodHandle add = ... (int x, int y) -> (x+y) ...;
   * assert(add.type().equals(intfn2));
   * MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
   * assert(twice.type().equals(intfn1));
   * assert((int)twice.invokeExact(21) == 42);
   * }</pre></blockquote>
   *
   * @param target the method handle to invoke after arguments are reordered
   * @param newType the expected type of the new method handle
   * @param reorder an index array which controls the reordering
   * @return a method handle which delegates to the target after it drops unused arguments and moves
   * and/or duplicates the other arguments
   * @throws NullPointerException if any argument is null
   * @throws IllegalArgumentException if the index array length is not equal to the arity of the
   * target, or if any index array element not a valid index for a parameter of {@code newType}, or
   * if two corresponding parameter types in {@code target.type()} and {@code newType} are not
   * identical,
   */
  public static MethodHandle permuteArguments(MethodHandle target, MethodType newType,
      int... reorder) {
    reorder = reorder.clone();  // get a private copy
    MethodType oldType = target.type();
    permuteArgumentChecks(reorder, newType, oldType);
    // first detect dropped arguments and handle them separately
    int[] originalReorder = reorder;
    BoundMethodHandle result = target.rebind();
    LambdaForm form = result.form;
    int newArity = newType.parameterCount();
    // Normalize the reordering into a real permutation,
    // by removing duplicates and adding dropped elements.
    // This somewhat improves lambda form caching, as well
    // as simplifying the transform by breaking it up into steps.
    for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
      if (ddIdx > 0) {
        // We found a duplicated entry at reorder[ddIdx].
        // Example:  (x,y,z)->asList(x,y,z)
        // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
        // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
        // The starred element corresponds to the argument
        // deleted by the dupArgumentForm transform.
        int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
        boolean killFirst = false;
        for (int val; (val = reorder[--dstPos]) != dupVal; ) {
          // Set killFirst if the dup is larger than an intervening position.
          // This will remove at least one inversion from the permutation.
          if (dupVal > val) {
            killFirst = true;
          }
        }
        if (!killFirst) {
          srcPos = dstPos;
          dstPos = ddIdx;
        }
        form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
        assert (reorder[srcPos] == reorder[dstPos]);
        oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
        // contract the reordering by removing the element at dstPos
        int tailPos = dstPos + 1;
        System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
        reorder = Arrays.copyOf(reorder, reorder.length - 1);
      } else {
        int dropVal = ~ddIdx, insPos = 0;
        while (insPos < reorder.length && reorder[insPos] < dropVal) {
          // Find first element of reorder larger than dropVal.
          // This is where we will insert the dropVal.
          insPos += 1;
        }
        Class<?> ptype = newType.parameterType(dropVal);
        form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
        oldType = oldType.insertParameterTypes(insPos, ptype);
        // expand the reordering by inserting an element at insPos
        int tailPos = insPos + 1;
        reorder = Arrays.copyOf(reorder, reorder.length + 1);
        System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
        reorder[insPos] = dropVal;
      }
      assert (permuteArgumentChecks(reorder, newType, oldType));
    }
    assert (reorder.length == newArity);  // a perfect permutation
    // Note:  This may cache too many distinct LFs. Consider backing off to varargs code.
    form = form.editor().permuteArgumentsForm(1, reorder);
    if (newType == result.type() && form == result.internalForm()) {
      return result;
    }
    return result.copyWith(newType, form);
  }

  /**
   * Return an indication of any duplicate or omission in reorder.
   * If the reorder contains a duplicate entry, return the index of the second occurrence.
   * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
   * Otherwise, return zero.
   * If an element not in [0..newArity-1] is encountered, return reorder.length.
   */
  private static int findFirstDupOrDrop(int[] reorder, int newArity) {
    final int BIT_LIMIT = 63;  // max number of bits in bit mask
    if (newArity < BIT_LIMIT) {
      long mask = 0;
      for (int i = 0; i < reorder.length; i++) {
        int arg = reorder[i];
        if (arg >= newArity) {
          return reorder.length;
        }
        long bit = 1L << arg;
        if ((mask & bit) != 0) {
          return i;  // >0 indicates a dup
        }
        mask |= bit;
      }
      if (mask == (1L << newArity) - 1) {
        assert (Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
        return 0;
      }
      // find first zero
      long zeroBit = Long.lowestOneBit(~mask);
      int zeroPos = Long.numberOfTrailingZeros(zeroBit);
      assert (zeroPos <= newArity);
      if (zeroPos == newArity) {
        return 0;
      }
      return ~zeroPos;
    } else {
      // same algorithm, different bit set
      BitSet mask = new BitSet(newArity);
      for (int i = 0; i < reorder.length; i++) {
        int arg = reorder[i];
        if (arg >= newArity) {
          return reorder.length;
        }
        if (mask.get(arg)) {
          return i;  // >0 indicates a dup
        }
        mask.set(arg);
      }
      int zeroPos = mask.nextClearBit(0);
      assert (zeroPos <= newArity);
      if (zeroPos == newArity) {
        return 0;
      }
      return ~zeroPos;
    }
  }

  private static boolean permuteArgumentChecks(int[] reorder, MethodType newType,
      MethodType oldType) {
    if (newType.returnType() != oldType.returnType()) {
      throw newIllegalArgumentException("return types do not match",
          oldType, newType);
    }
    if (reorder.length == oldType.parameterCount()) {
      int limit = newType.parameterCount();
      boolean bad = false;
      for (int j = 0; j < reorder.length; j++) {
        int i = reorder[j];
        if (i < 0 || i >= limit) {
          bad = true;
          break;
        }
        Class<?> src = newType.parameterType(i);
        Class<?> dst = oldType.parameterType(j);
        if (src != dst) {
          throw newIllegalArgumentException("parameter types do not match after reorder",
              oldType, newType);
        }
      }
      if (!bad) {
        return true;
      }
    }
    throw newIllegalArgumentException("bad reorder array: " + Arrays.toString(reorder));
  }

  /**
   * Produces a method handle of the requested return type which returns the given
   * constant value every time it is invoked.
   * <p>
   * Before the method handle is returned, the passed-in value is converted to the requested type.
   * If the requested type is primitive, widening primitive conversions are attempted,
   * else reference conversions are attempted.
   * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
   *
   * @param type the return type of the desired method handle
   * @param value the value to return
   * @return a method handle of the given return type and no arguments, which always returns the
   * given value
   * @throws NullPointerException if the {@code type} argument is null
   * @throws ClassCastException if the value cannot be converted to the required return type
   * @throws IllegalArgumentException if the given type is {@code void.class}
   */
  public static MethodHandle constant(Class<?> type, Object value) {
    if (type.isPrimitive()) {
      if (type == void.class) {
        throw newIllegalArgumentException("void type");
      }
      Wrapper w = Wrapper.forPrimitiveType(type);
      value = w.convert(value, type);
      if (w.zero().equals(value)) {
        return zero(w, type);
      }
      return insertArguments(identity(type), 0, value);
    } else {
      if (value == null) {
        return zero(Wrapper.OBJECT, type);
      }
      return identity(type).bindTo(value);
    }
  }

  /**
   * Produces a method handle which returns its sole argument when invoked.
   *
   * @param type the type of the sole parameter and return value of the desired method handle
   * @return a unary method handle which accepts and returns the given type
   * @throws NullPointerException if the argument is null
   * @throws IllegalArgumentException if the given type is {@code void.class}
   */
  public static MethodHandle identity(Class<?> type) {
    Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
    int pos = btw.ordinal();
    MethodHandle ident = IDENTITY_MHS[pos];
    if (ident == null) {
      ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
    }
    if (ident.type().returnType() == type) {
      return ident;
    }
    // something like identity(Foo.class); do not bother to intern these
    assert (btw == Wrapper.OBJECT);
    return makeIdentity(type);
  }

  private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.values().length];

  private static MethodHandle makeIdentity(Class<?> ptype) {
    MethodType mtype = MethodType.methodType(ptype, ptype);
    LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
    return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
  }

  private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
    int pos = btw.ordinal();
    MethodHandle zero = ZERO_MHS[pos];
    if (zero == null) {
      zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
    }
    if (zero.type().returnType() == rtype) {
      return zero;
    }
    assert (btw == Wrapper.OBJECT);
    return makeZero(rtype);
  }

  private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.values().length];

  private static MethodHandle makeZero(Class<?> rtype) {
    MethodType mtype = MethodType.methodType(rtype);
    LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
    return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
  }

  synchronized private static MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos,
      MethodHandle value) {
    // Simulate a CAS, to avoid racy duplication of results.
    MethodHandle prev = cache[pos];
    if (prev != null) {
      return prev;
    }
    return cache[pos] = value;
  }

  /**
   * Provides a target method handle with one or more <em>bound arguments</em>
   * in advance of the method handle's invocation.
   * The formal parameters to the target corresponding to the bound
   * arguments are called <em>bound parameters</em>.
   * Returns a new method handle which saves away the bound arguments.
   * When it is invoked, it receives arguments for any non-bound parameters,
   * binds the saved arguments to their corresponding parameters,
   * and calls the original target.
   * <p>
   * The type of the new method handle will drop the types for the bound
   * parameters from the original target type, since the new method handle
   * will no longer require those arguments to be supplied by its callers.
   * <p>
   * Each given argument object must match the corresponding bound parameter type.
   * If a bound parameter type is a primitive, the argument object
   * must be a wrapper, and will be unboxed to produce the primitive value.
   * <p>
   * The {@code pos} argument selects which parameters are to be bound.
   * It may range between zero and <i>N-L</i> (inclusively),
   * where <i>N</i> is the arity of the target method handle
   * and <i>L</i> is the length of the values array.
   *
   * @param target the method handle to invoke after the argument is inserted
   * @param pos where to insert the argument (zero for the first)
   * @param values the series of arguments to insert
   * @return a method handle which inserts an additional argument, before calling the original
   * method handle
   * @throws NullPointerException if the target or the {@code values} array is null
   * @see MethodHandle#bindTo
   */
  public static MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
    int insCount = values.length;
    Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
    if (insCount == 0) {
      return target;
    }
    BoundMethodHandle result = target.rebind();
    for (int i = 0; i < insCount; i++) {
      Object value = values[i];
      Class<?> ptype = ptypes[pos + i];
      if (ptype.isPrimitive()) {
        result = insertArgumentPrimitive(result, pos, ptype, value);
      } else {
        value = ptype.cast(value);  // throw CCE if needed
        result = result.bindArgumentL(pos, value);
      }
    }
    return result;
  }

  private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
      Class<?> ptype, Object value) {
    Wrapper w = Wrapper.forPrimitiveType(ptype);
    // perform unboxing and/or primitive conversion
    value = w.convert(value, ptype);
    switch (w) {
      case INT:
        return result.bindArgumentI(pos, (int) value);
      case LONG:
        return result.bindArgumentJ(pos, (long) value);
      case FLOAT:
        return result.bindArgumentF(pos, (float) value);
      case DOUBLE:
        return result.bindArgumentD(pos, (double) value);
      default:
        return result.bindArgumentI(pos, ValueConversions.widenSubword(value));
    }
  }

  private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos)
      throws RuntimeException {
    MethodType oldType = target.type();
    int outargs = oldType.parameterCount();
    int inargs = outargs - insCount;
    if (inargs < 0) {
      throw newIllegalArgumentException("too many values to insert");
    }
    if (pos < 0 || pos > inargs) {
      throw newIllegalArgumentException("no argument type to append");
    }
    return oldType.ptypes();
  }

  /**
   * Produces a method handle which will discard some dummy arguments before calling some other
   * specified <i>target</i> method handle. The type of the new method handle will be the same as
   * the target's type, except it will also include the dummy argument types, at some given
   * position. <p> The {@code pos} argument may range between zero and <i>N</i>, where <i>N</i> is
   * the arity of the target. If {@code pos} is zero, the dummy arguments will precede the target's
   * real arguments; if {@code pos} is <i>N</i> they will come after. <p> <b>Example:</b>
   * <blockquote><pre>{@code
   * import static java.lang.invoke.MethodHandles.*;
   * import static java.lang.invoke.MethodType.*;
   * ...
   * MethodHandle cat = lookup().findVirtual(String.class,
   * "concat", methodType(String.class, String.class));
   * assertEquals("xy", (String) cat.invokeExact("x", "y"));
   * MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
   * MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
   * assertEquals(bigType, d0.type());
   * assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
   * }</pre></blockquote>
   * <p> This method is also equivalent to the following code:
   * <blockquote><pre>
   * {@link #dropArguments(MethodHandle, int, Class...) dropArguments}{@code (target, pos,
   * valueTypes.toArray(new Class[0]))}
   * </pre></blockquote>
   *
   * @param target the method handle to invoke after the arguments are dropped
   * @param valueTypes the type(s) of the argument(s) to drop
   * @param pos position of first argument to drop (zero for the leftmost)
   * @return a method handle which drops arguments of the given types, before calling the original
   * method handle
   * @throws NullPointerException if the target is null, or if the {@code valueTypes} list or any of
   * its elements is null
   * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class}, or
   * if {@code pos} is negative or greater than the arity of the target, or if the new method
   * handle's type would have too many parameters
   */
  public static MethodHandle dropArguments(MethodHandle target, int pos,
      List<Class<?>> valueTypes) {
    MethodType oldType = target.type();  // get NPE
    int dropped = dropArgumentChecks(oldType, pos, valueTypes);
    MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
    if (dropped == 0) {
      return target;
    }
    BoundMethodHandle result = target.rebind();
    LambdaForm lform = result.form;
    int insertFormArg = 1 + pos;
    for (Class<?> ptype : valueTypes) {
      lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
    }
    result = result.copyWith(newType, lform);
    return result;
  }

  private static int dropArgumentChecks(MethodType oldType, int pos, List<Class<?>> valueTypes) {
    int dropped = valueTypes.size();
    MethodType.checkSlotCount(dropped);
    int outargs = oldType.parameterCount();
    int inargs = outargs + dropped;
    if (pos < 0 || pos > outargs) {
      throw newIllegalArgumentException("no argument type to remove"
          + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
      );
    }
    return dropped;
  }

  /**
   * Produces a method handle which will discard some dummy arguments before calling some other
   * specified <i>target</i> method handle. The type of the new method handle will be the same as
   * the target's type, except it will also include the dummy argument types, at some given
   * position. <p> The {@code pos} argument may range between zero and <i>N</i>, where <i>N</i> is
   * the arity of the target. If {@code pos} is zero, the dummy arguments will precede the target's
   * real arguments; if {@code pos} is <i>N</i> they will come after. <p> <b>Example:</b>
   * <blockquote><pre>{@code
   * import static java.lang.invoke.MethodHandles.*;
   * import static java.lang.invoke.MethodType.*;
   * ...
   * MethodHandle cat = lookup().findVirtual(String.class,
   * "concat", methodType(String.class, String.class));
   * assertEquals("xy", (String) cat.invokeExact("x", "y"));
   * MethodHandle d0 = dropArguments(cat, 0, String.class);
   * assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
   * MethodHandle d1 = dropArguments(cat, 1, String.class);
   * assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
   * MethodHandle d2 = dropArguments(cat, 2, String.class);
   * assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
   * MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
   * assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
   * }</pre></blockquote>
   * <p> This method is also equivalent to the following code:
   * <blockquote><pre>
   * {@link #dropArguments(MethodHandle, int, List) dropArguments}{@code (target, pos,
   * Arrays.asList(valueTypes))}
   * </pre></blockquote>
   *
   * @param target the method handle to invoke after the arguments are dropped
   * @param valueTypes the type(s) of the argument(s) to drop
   * @param pos position of first argument to drop (zero for the leftmost)
   * @return a method handle which drops arguments of the given types, before calling the original
   * method handle
   * @throws NullPointerException if the target is null, or if the {@code valueTypes} array or any
   * of its elements is null
   * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class}, or
   * if {@code pos} is negative or greater than the arity of the target, or if the new method
   * handle's type would have <a href="MethodHandle.html#maxarity">too many parameters</a>
   */
  public static MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
    return dropArguments(target, pos, Arrays.asList(valueTypes));
  }

  /**
   * Adapts a target method handle by pre-processing
   * one or more of its arguments, each with its own unary filter function,
   * and then calling the target with each pre-processed argument
   * replaced by the result of its corresponding filter function.
   * <p>
   * The pre-processing is performed by one or more method handles,
   * specified in the elements of the {@code filters} array.
   * The first element of the filter array corresponds to the {@code pos}
   * argument of the target, and so on in sequence.
   * <p>
   * Null arguments in the array are treated as identity functions,
   * and the corresponding arguments left unchanged.
   * (If there are no non-null elements in the array, the original target is returned.)
   * Each filter is applied to the corresponding argument of the adapter.
   * <p>
   * If a filter {@code F} applies to the {@code N}th argument of
   * the target, then {@code F} must be a method handle which
   * takes exactly one argument.  The type of {@code F}'s sole argument
   * replaces the corresponding argument type of the target
   * in the resulting adapted method handle.
   * The return type of {@code F} must be identical to the corresponding
   * parameter type of the target.
   * <p>
   * It is an error if there are elements of {@code filters}
   * (null or not)
   * which do not correspond to argument positions in the target.
   * <p><b>Example:</b>
   * <blockquote><pre>{@code
   * import static java.lang.invoke.MethodHandles.*;
   * import static java.lang.invoke.MethodType.*;
   * ...
   * MethodHandle cat = lookup().findVirtual(String.class,
   * "concat", methodType(String.class, String.class));
   * MethodHandle upcase = lookup().findVirtual(String.class,
   * "toUpperCase", methodType(String.class));
   * assertEquals("xy", (String) cat.invokeExact("x", "y"));
   * MethodHandle f0 = filterArguments(cat, 0, upcase);
   * assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
   * MethodHandle f1 = filterArguments(cat, 1, upcase);
   * assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
   * MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
   * assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
   * }</pre></blockquote>
   * <p> Here is pseudocode for the resulting adapter:
   * <blockquote><pre>{@code
   * V target(P... p, A[i]... a[i], B... b);
   * A[i] filter[i](V[i]);
   * T adapter(P... p, V[i]... v[i], B... b) {
   *   return target(p..., f[i](v[i])..., b...);
   * }
   * }</pre></blockquote>
   *
   * @param target the method handle to invoke after arguments are filtered
   * @param pos the position of the first argument to filter
   * @param filters method handles to call initially on filtered arguments
   * @return method handle which incorporates the specified argument filtering logic
   * @throws NullPointerException if the target is null or if the {@code filters} array is null
   * @throws IllegalArgumentException if a non-null element of {@code filters} does not match a
   * corresponding argument type of target as described above, or if the {@code pos+filters.length}
   * is greater than {@code target.type().parameterCount()}, or if the resulting method handle's
   * type would have <a href="MethodHandle.html#maxarity">too many parameters</a>
   */
  public static MethodHandle filterArguments(MethodHandle target, int pos,
      MethodHandle... filters) {
    filterArgumentsCheckArity(target, pos, filters);
    MethodHandle adapter = target;
    int curPos = pos - 1;  // pre-incremented
    for (MethodHandle filter : filters) {
      curPos += 1;
      if (filter == null) {
        continue;  // ignore null elements of filters
      }
      adapter = filterArgument(adapter, curPos, filter);
    }
    return adapter;
  }

  /*non-public*/
  static MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
    filterArgumentChecks(target, pos, filter);
    MethodType targetType = target.type();
    MethodType filterType = filter.type();
    BoundMethodHandle result = target.rebind();
    Class<?> newParamType = filterType.parameterType(0);
    LambdaForm lform = result.editor()
        .filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
    MethodType newType = targetType.changeParameterType(pos, newParamType);
    result = result.copyWithExtendL(newType, lform, filter);
    return result;
  }

  private static void filterArgumentsCheckArity(MethodHandle target, int pos,
      MethodHandle[] filters) {
    MethodType targetType = target.type();
    int maxPos = targetType.parameterCount();
    if (pos + filters.length > maxPos) {
      throw newIllegalArgumentException("too many filters");
    }
  }

  private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter)
      throws RuntimeException {
    MethodType targetType = target.type();
    MethodType filterType = filter.type();
    if (filterType.parameterCount() != 1
        || filterType.returnType() != targetType.parameterType(pos)) {
      throw newIllegalArgumentException("target and filter types do not match", targetType,
          filterType);
    }
  }

  /**
   * Adapts a target method handle by pre-processing
   * a sub-sequence of its arguments with a filter (another method handle).
   * The pre-processed arguments are replaced by the result (if any) of the
   * filter function.
   * The target is then called on the modified (usually shortened) argument list.
   * <p>
   * If the filter returns a value, the target must accept that value as
   * its argument in position {@code pos}, preceded and/or followed by
   * any arguments not passed to the filter.
   * If the filter returns void, the target must accept all arguments
   * not passed to the filter.
   * No arguments are reordered, and a result returned from the filter
   * replaces (in order) the whole subsequence of arguments originally
   * passed to the adapter.
   * <p>
   * The argument types (if any) of the filter
   * replace zero or one argument types of the target, at position {@code pos},
   * in the resulting adapted method handle.
   * The return type of the filter (if any) must be identical to the
   * argument type of the target at position {@code pos}, and that target argument
   * is supplied by the return value of the filter.
   * <p>
   * In all cases, {@code pos} must be greater than or equal to zero, and
   * {@code pos} must also be less than or equal to the target's arity.
   * <p><b>Example:</b>
   * <blockquote><pre>{@code
   * import static java.lang.invoke.MethodHandles.*;
   * import static java.lang.invoke.MethodType.*;
   * ...
   * MethodHandle deepToString = publicLookup()
   * .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
   *
   * MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
   * assertEquals("[strange]", (String) ts1.invokeExact("strange"));
   *
   * MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
   * assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
   *
   * MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
   * MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
   * assertEquals("[top, [up, down], strange]",
   * (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
   *
   * MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
   * assertEquals("[top, [up, down], [strange]]",
   * (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
   *
   * MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
   * assertEquals("[top, [[up, down, strange], charm], bottom]",
   * (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
   * }</pre></blockquote>
   * <p> Here is pseudocode for the resulting adapter:
   * <blockquote><pre>{@code
   * T target(A...,V,C...);
   * V filter(B...);
   * T adapter(A... a,B... b,C... c) {
   *   V v = filter(b...);
   *   return target(a...,v,c...);
   * }
   * // and if the filter has no arguments:
   * T target2(A...,V,C...);
   * V filter2();
   * T adapter2(A... a,C... c) {
   *   V v = filter2();
   *   return target2(a...,v,c...);
   * }
   * // and if the filter has a void return:
   * T target3(A...,C...);
   * void filter3(B...);
   * void adapter3(A... a,B... b,C... c) {
   *   filter3(b...);
   *   return target3(a...,c...);
   * }
   * }</pre></blockquote>
   * <p>
   * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
   * one which first "folds" the affected arguments, and then drops them, in separate
   * steps as follows:
   * <blockquote><pre>{@code
   * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
   * mh = MethodHandles.foldArguments(mh, coll); //step 1
   * }</pre></blockquote>
   * If the target method handle consumes no arguments besides than the result
   * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
   * is equivalent to {@code filterReturnValue(coll, mh)}.
   * If the filter method handle {@code coll} consumes one argument and produces
   * a non-void result, then {@code collectArguments(mh, N, coll)}
   * is equivalent to {@code filterArguments(mh, N, coll)}.
   * Other equivalences are possible but would require argument permutation.
   *
   * @param target the method handle to invoke after filtering the subsequence of arguments
   * @param pos the position of the first adapter argument to pass to the filter, and/or the target
   * argument which receives the result of the filter
   * @param filter method handle to call on the subsequence of arguments
   * @return method handle which incorporates the specified argument subsequence filtering logic
   * @throws NullPointerException if either argument is null
   * @throws IllegalArgumentException if the return type of {@code filter} is non-void and is not
   * the same as the {@code pos} argument of the target, or if {@code pos} is not between 0 and the
   * target's arity, inclusive, or if the resulting method handle's type would have <a
   * href="MethodHandle.html#maxarity">too many parameters</a>
   * @see MethodHandles#foldArguments
   * @see MethodHandles#filterArguments
   * @see MethodHandles#filterReturnValue
   */
  public static MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
    MethodType newType = collectArgumentsChecks(target, pos, filter);
    MethodType collectorType = filter.type();
    BoundMethodHandle result = target.rebind();
    LambdaForm lform;
    if (collectorType.returnType().isArray() && filter.intrinsicName() == Intrinsic.NEW_ARRAY) {
      lform = result.editor().collectArgumentArrayForm(1 + pos, filter);
      if (lform != null) {
        return result.copyWith(newType, lform);
      }
    }
    lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
    return result.copyWithExtendL(newType, lform, filter);
  }

  private static MethodType collectArgumentsChecks(MethodHandle target, int pos,
      MethodHandle filter) throws RuntimeException {
    MethodType targetType = target.type();
    MethodType filterType = filter.type();
    Class<?> rtype = filterType.returnType();
    List<Class<?>> filterArgs = filterType.parameterList();
    if (rtype == void.class) {
      return targetType.insertParameterTypes(pos, filterArgs);
    }
    if (rtype != targetType.parameterType(pos)) {
      throw newIllegalArgumentException("target and filter types do not match", targetType,
          filterType);
    }
    return targetType.dropParameterTypes(pos, pos + 1).insertParameterTypes(pos, filterArgs);
  }

  /**
   * Adapts a target method handle by post-processing
   * its return value (if any) with a filter (another method handle).
   * The result of the filter is returned from the adapter.
   * <p>
   * If the target returns a value, the filter must accept that value as
   * its only argument.
   * If the target returns void, the filter must accept no arguments.
   * <p>
   * The return type of the filter
   * replaces the return type of the target
   * in the resulting adapted method handle.
   * The argument type of the filter (if any) must be identical to the
   * return type of the target.
   * <p><b>Example:</b>
   * <blockquote><pre>{@code
   * import static java.lang.invoke.MethodHandles.*;
   * import static java.lang.invoke.MethodType.*;
   * ...
   * MethodHandle cat = lookup().findVirtual(String.class,
   * "concat", methodType(String.class, String.class));
   * MethodHandle length = lookup().findVirtual(String.class,
   * "length", methodType(int.class));
   * System.out.println((String) cat.invokeExact("x", "y")); // xy
   * MethodHandle f0 = filterReturnValue(cat, length);
   * System.out.println((int) f0.invokeExact("x", "y")); // 2
   * }</pre></blockquote>
   * <p> Here is pseudocode for the resulting adapter:
   * <blockquote><pre>{@code
   * V target(A...);
   * T filter(V);
   * T adapter(A... a) {
   *   V v = target(a...);
   *   return filter(v);
   * }
   * // and if the target has a void return:
   * void target2(A...);
   * T filter2();
   * T adapter2(A... a) {
   *   target2(a...);
   *   return filter2();
   * }
   * // and if the filter has a void return:
   * V target3(A...);
   * void filter3(V);
   * void adapter3(A... a) {
   *   V v = target3(a...);
   *   filter3(v);
   * }
   * }</pre></blockquote>
   *
   * @param target the method handle to invoke before filtering the return value
   * @param filter method handle to call on the return value
   * @return method handle which incorporates the specified return value filtering logic
   * @throws NullPointerException if either argument is null
   * @throws IllegalArgumentException if the argument list of {@code filter} does not match the
   * return type of target as described above
   */
  public static MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
    MethodType targetType = target.type();
    MethodType filterType = filter.type();
    filterReturnValueChecks(targetType, filterType);
    BoundMethodHandle result = target.rebind();
    BasicType rtype = BasicType.basicType(filterType.returnType());
    LambdaForm lform = result.editor().filterReturnForm(rtype, false);
    MethodType newType = targetType.changeReturnType(filterType.returnType());
    result = result.copyWithExtendL(newType, lform, filter);
    return result;
  }

  private static void filterReturnValueChecks(MethodType targetType, MethodType filterType)
      throws RuntimeException {
    Class<?> rtype = targetType.returnType();
    int filterValues = filterType.parameterCount();
    if (filterValues == 0
        ? (rtype != void.class)
        : (rtype != filterType.parameterType(0))) {
      throw newIllegalArgumentException("target and filter types do not match", targetType,
          filterType);
    }
  }

  /**
   * Adapts a target method handle by pre-processing some of its arguments, and then calling the
   * target with the result of the pre-processing, inserted into the original sequence of arguments.
   * <p> The pre-processing is performed by {@code combiner}, a second method handle. Of the
   * arguments passed to the adapter, the first {@code N} arguments are copied to the combiner,
   * which is then called. (Here, {@code N} is defined as the parameter count of the combiner.)
   * After this, control passes to the target, with any result from the combiner inserted before the
   * original {@code N} incoming arguments. <p> If the combiner returns a value, the first parameter
   * type of the target must be identical with the return type of the combiner, and the next {@code
   * N} parameter types of the target must exactly match the parameters of the combiner. <p> If the
   * combiner has a void return, no result will be inserted, and the first {@code N} parameter types
   * of the target must exactly match the parameters of the combiner. <p> The resulting adapter is
   * the same type as the target, except that the first parameter type is dropped, if it corresponds
   * to the result of the combiner. <p> (Note that {@link #dropArguments(MethodHandle, int, List)
   * dropArguments} can be used to remove any arguments that either the combiner or the target does
   * not wish to receive. If some of the incoming arguments are destined only for the combiner,
   * consider using {@link MethodHandle#asCollector asCollector} instead, since those arguments will
   * not need to be live on the stack on entry to the target.) <p><b>Example:</b>
   * <blockquote><pre>{@code
   * import static java.lang.invoke.MethodHandles.*;
   * import static java.lang.invoke.MethodType.*;
   * ...
   * MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
   * "println", methodType(void.class, String.class))
   * .bindTo(System.out);
   * MethodHandle cat = lookup().findVirtual(String.class,
   * "concat", methodType(String.class, String.class));
   * assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
   * MethodHandle catTrace = foldArguments(cat, trace);
   * // also prints "boo":
   * assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
   * }</pre></blockquote>
   * <p> Here is pseudocode for the resulting adapter:
   * <blockquote><pre>{@code
   * // there are N arguments in A...
   * T target(V, A[N]..., B...);
   * V combiner(A...);
   * T adapter(A... a, B... b) {
   *   V v = combiner(a...);
   *   return target(v, a..., b...);
   * }
   * // and if the combiner has a void return:
   * T target2(A[N]..., B...);
   * void combiner2(A...);
   * T adapter2(A... a, B... b) {
   *   combiner2(a...);
   *   return target2(a..., b...);
   * }
   * }</pre></blockquote>
   *
   * @param target the method handle to invoke after arguments are combined
   * @param combiner method handle to call initially on the incoming arguments
   * @return method handle which incorporates the specified argument folding logic
   * @throws NullPointerException if either argument is null
   * @throws IllegalArgumentException if {@code combiner}'s return type is non-void and not the same
   * as the first argument type of the target, or if the initial {@code N} argument types of the
   * target (skipping one matching the {@code combiner}'s return type) are not identical with the
   * argument types of {@code combiner}
   */
  public static MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
    int foldPos = 0;
    MethodType targetType = target.type();
    MethodType combinerType = combiner.type();
    Class<?> rtype = foldArgumentChecks(foldPos, targetType, combinerType);
    BoundMethodHandle result = target.rebind();
    boolean dropResult = (rtype == void.class);
    // Note:  This may cache too many distinct LFs. Consider backing off to varargs code.
    LambdaForm lform = result.editor()
        .foldArgumentsForm(1 + foldPos, dropResult, combinerType.basicType());
    MethodType newType = targetType;
    if (!dropResult) {
      newType = newType.dropParameterTypes(foldPos, foldPos + 1);
    }
    result = result.copyWithExtendL(newType, lform, combiner);
    return result;
  }

  private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType,
      MethodType combinerType) {
    int foldArgs = combinerType.parameterCount();
    Class<?> rtype = combinerType.returnType();
    int foldVals = rtype == void.class ? 0 : 1;
    int afterInsertPos = foldPos + foldVals;
    boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
    if (ok && !(combinerType.parameterList()
        .equals(targetType.parameterList().subList(afterInsertPos,
            afterInsertPos + foldArgs)))) {
      ok = false;
    }
    if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(0)) {
      ok = false;
    }
    if (!ok) {
      throw misMatchedTypes("target and combiner types", targetType, combinerType);
    }
    return rtype;
  }

  /**
   * Makes a method handle which adapts a target method handle,
   * by guarding it with a test, a boolean-valued method handle.
   * If the guard fails, a fallback handle is called instead.
   * All three method handles must have the same corresponding
   * argument and return types, except that the return type
   * of the test must be boolean, and the test is allowed
   * to have fewer arguments than the other two method handles.
   * <p> Here is pseudocode for the resulting adapter:
   * <blockquote><pre>{@code
   * boolean test(A...);
   * T target(A...,B...);
   * T fallback(A...,B...);
   * T adapter(A... a,B... b) {
   *   if (test(a...))
   *     return target(a..., b...);
   *   else
   *     return fallback(a..., b...);
   * }
   * }</pre></blockquote>
   * Note that the test arguments ({@code a...} in the pseudocode) cannot
   * be modified by execution of the test, and so are passed unchanged
   * from the caller to the target or fallback as appropriate.
   *
   * @param test method handle used for test, must return boolean
   * @param target method handle to call if test passes
   * @param fallback method handle to call if test fails
   * @return method handle which incorporates the specified if/then/else logic
   * @throws NullPointerException if any argument is null
   * @throws IllegalArgumentException if {@code test} does not return boolean, or if all three
   * method types do not match (with the return type of {@code test} changed to match that of the
   * target).
   */
  public static MethodHandle guardWithTest(MethodHandle test,
      MethodHandle target,
      MethodHandle fallback) {
    MethodType gtype = test.type();
    MethodType ttype = target.type();
    MethodType ftype = fallback.type();
    if (!ttype.equals(ftype)) {
      throw misMatchedTypes("target and fallback types", ttype, ftype);
    }
    if (gtype.returnType() != boolean.class) {
      throw newIllegalArgumentException("guard type is not a predicate " + gtype);
    }
    List<Class<?>> targs = ttype.parameterList();
    List<Class<?>> gargs = gtype.parameterList();
    if (!targs.equals(gargs)) {
      int gpc = gargs.size(), tpc = targs.size();
      if (gpc >= tpc || !targs.subList(0, gpc).equals(gargs)) {
        throw misMatchedTypes("target and test types", ttype, gtype);
      }
      test = dropArguments(test, gpc, targs.subList(gpc, tpc));
      gtype = test.type();
    }
    return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
  }

  static RuntimeException misMatchedTypes(String what, MethodType t1, MethodType t2) {
    return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
  }

  /**
   * Makes a method handle which adapts a target method handle,
   * by running it inside an exception handler.
   * If the target returns normally, the adapter returns that value.
   * If an exception matching the specified type is thrown, the fallback
   * handle is called instead on the exception, plus the original arguments.
   * <p>
   * The target and handler must have the same corresponding
   * argument and return types, except that handler may omit trailing arguments
   * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
   * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
   * <p> Here is pseudocode for the resulting adapter:
   * <blockquote><pre>{@code
   * T target(A..., B...);
   * T handler(ExType, A...);
   * T adapter(A... a, B... b) {
   *   try {
   *     return target(a..., b...);
   *   } catch (ExType ex) {
   *     return handler(ex, a...);
   *   }
   * }
   * }</pre></blockquote>
   * Note that the saved arguments ({@code a...} in the pseudocode) cannot
   * be modified by execution of the target, and so are passed unchanged
   * from the caller to the handler, if the handler is invoked.
   * <p>
   * The target and handler must return the same type, even if the handler
   * always throws.  (This might happen, for instance, because the handler
   * is simulating a {@code finally} clause).
   * To create such a throwing handler, compose the handler creation logic
   * with {@link #throwException throwException},
   * in order to create a method handle of the correct return type.
   *
   * @param target method handle to call
   * @param exType the type of exception which the handler will catch
   * @param handler method handle to call if a matching exception is thrown
   * @return method handle which incorporates the specified try/catch logic
   * @throws NullPointerException if any argument is null
   * @throws IllegalArgumentException if {@code handler} does not accept the given exception type,
   * or if the method handle types do not match in their return types and their corresponding
   * parameters
   */
  public static MethodHandle catchException(MethodHandle target,
      Class<? extends Throwable> exType,
      MethodHandle handler) {
    MethodType ttype = target.type();
    MethodType htype = handler.type();
    if (htype.parameterCount() < 1 ||
        !htype.parameterType(0).isAssignableFrom(exType)) {
      throw newIllegalArgumentException("handler does not accept exception type " + exType);
    }
    if (htype.returnType() != ttype.returnType()) {
      throw misMatchedTypes("target and handler return types", ttype, htype);
    }
    List<Class<?>> targs = ttype.parameterList();
    List<Class<?>> hargs = htype.parameterList();
    hargs = hargs.subList(1, hargs.size());  // omit leading parameter from handler
    if (!targs.equals(hargs)) {
      int hpc = hargs.size(), tpc = targs.size();
      if (hpc >= tpc || !targs.subList(0, hpc).equals(hargs)) {
        throw misMatchedTypes("target and handler types", ttype, htype);
      }
      handler = dropArguments(handler, 1 + hpc, targs.subList(hpc, tpc));
      htype = handler.type();
    }
    return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
  }

  /**
   * Produces a method handle which will throw exceptions of the given {@code exType}.
   * The method handle will accept a single argument of {@code exType},
   * and immediately throw it as an exception.
   * The method type will nominally specify a return of {@code returnType}.
   * The return type may be anything convenient:  It doesn't matter to the
   * method handle's behavior, since it will never return normally.
   *
   * @param returnType the return type of the desired method handle
   * @param exType the parameter type of the desired method handle
   * @return method handle which can throw the given exceptions
   * @throws NullPointerException if either argument is null
   */
  public static MethodHandle throwException(Class<?> returnType,
      Class<? extends Throwable> exType) {
    if (!Throwable.class.isAssignableFrom(exType)) {
      throw new ClassCastException(exType.getName());
    }
    return MethodHandleImpl.throwException(MethodType.methodType(returnType, exType));
  }
}
